I think the problem with the 90's anime isn't that they do too many redemptions but
who they pick and choose to redeem in the first place, while most of their choices work, alot of them also come off as just really bizarre and forced.
For example it still baffles me to this day why 90's anime Beryl wasn't redeemed and that she was made even
less sympathetic than her manga counterpart, when actually Manga!Beryl’s story would've fit better in the 90's anime while the actual 90's Beryl was a better fit for the manga. Same goes for Rubeus, why was he the only one of the clan not portrayed as even remotely sympathetic in the 90's anime? By contrast Manga!Rubeus is probably the only sympathetic Clan member, it's like their versions were switched.
There was never any attempt at redeeming Esmeraude, Eudial, Mimette or Kunzite either despite all 4 showing very sympathetic & relatable traits, yet Tigers Eye & Hawk's Eye get to ride-off the coattails of Fish-Eye's well earned redemption when they were sexist, pick-up artist creeps? Buh?
See alot of the redemptions just plain don't make sense and feel unearned, Galaxia being the biggest example of this and the worst offender, though honestly with her can you even really say she was redeemed when the 90's anime says she was never even evil in the first place and just "possessed?" Does her story even count as a redemption?
She was very emo she was basically a angsty girl who had it bad on her planet and basically sees everything as trash. I think that anime Galaxia was much better and more interesting.
At least Manga Galaxia actually had a personality and character, as opposed to her 90's counterpart who we know nothing about considering she was possessed by Chaos until the last few seconds of her screentime.
Another thing the reformed villians that don't die, they are all but forgotten. Why not use them in future arcs. Ali and An never comeback but they are in far off space so that excusable, but the Spectre Sisters they are turned into normal humans living in Judan as makeup sales women, what is their excuse? Why aren't the Amazoness Quarter appear in Stars like their manga counterparts, they even said they would all meet again.
At least Fairy Tail in most occasion after they reform their villains, they make use of them as allies in future arcs. Why doesn't Sailor Moon do that.
They rush there redemption stories with no real build up, and after that they are disguarded.
This is probably an unfortunate side-effect of the 90's anime itself being light on continuity. Each season is meant to be fairly self-contained with sparse references to the last compared to the manga's continuous, linear story.
To me, Usagi had every right to kill Beryl without hesitation in the anime (and Minako had no business doing it for her). This was the woman who destroyed the life she once led out of hate and jealousy, and now threatens to do the same thing with her current life. No other villain that Usagi faced since was ever more personal than Beryl and Metaria.
No Venus definitely deserved that kill, it showcased her rightful status as Leader of the Inners and personal protector of her most precious person, the Princess. It was the perfect bookend to her training days as Sailor V, and reading the Dark Kingdom arc right after Sailor V makes her kill all the more satisfying. Plus it's shown that she was the one who killed Beryl in the past in the exact same way, so it's meant to serve as a parallel and echo the themes of the past inevitably repeating that the 1st arc tackles.
In the manga Galaxia was born alone and remained isolated for a long time in that deserted little wasteland of a planet. Like Neptune said once: "anyone's heart would become cold after being alone for so long." Add to that traumatic past an extreme power-hungry disposition, grandiose delusions of the God complex variety, some malicious manipulation from Wiseman, and magical powers and you have the perfect Evil Overlord. So I wouldn't say she was just "emo".
But I agree that a possessed/corrupted Galaxia was interesting, and I liked the fact that Usagi/Sailor Moon/Serenity peacefully defeated her by literally lending Galaxia a hand - while the bloodiest of battles failed to finish her - because that's the essence of Usagi's power and heroism. Galaxia's redemption was a logical outcome because she wasn't responsible for anything she had done after her sacrifice to end the mother of all wars. If I had a complaint about the final battle arc of the Star season was that it dragged a bit too much before reaching its climax with Uranus and Neptune's deaths, thought the manga was way duller TBH.
BTW, wasn't manga Galaxia a bit of a case of Redemption Equals Death? I tend to like these, however I've never thought much of Galaxia in the manga continuity. Even with the explanation of her past and bits of character development she was basically reduced to arcade game super-villain
Galaxia in the manga was sooo much more than that, in fact I contend that not only was she easily the most complex & well done villain in Sailor Moon, but in fiction in general, that's right you heard me.
It really takes a 2nd read through of the manga in order to be able to pick up on the subtext, but Galaxia is great not just for all the reasons you mentioned but because she perfectly encapsulates the themes of the Stars arc on how being a Senshi isn't how it's all cracked up to be and is ultimately a cursed existence. What's great about Galaxia is she's just as much victim as she is villain. Her planet & Star Seed was heavily implied to be one of those weak-developing planets that the Galaxy Cauldron sometimes spits out and has failure to thrive, through no fault of her own she's been cast into this miserable existence because of the very system in place, she is a victim of the system and is little more than collateral damage in the Star-making process so she developed an inferiority complex which shaped her beliefs on everything. To her, only one's Sailor Crystal and their power is worth anything while the human flesh is worthless, because that's basically all that's defined her entire life and shaped her experiences. "Reject" Star Seeds like her are condemned to a miserable fate, while "Powerful" Star Seeds like the Sol System Senshi get to live it up, is it any wonder that one's Sailor Crystal is all she'd define one's worth by? In her eyes she's a walking example!
But the really great thing about Galaxia is that she doesn't just take this lying down, oh no, through sheer will-power she manages to train herself & her Sailor Crystal to unfathomable heights, to the point where she's now easily surpassing even the "healthy
" Star Seeds in power. She tries to start a revolution throughout the Galaxy, convincing them to revolt against the Galaxy Cauldron system and in return she'll give them Sailor Crystals and make them into Senshi, because everyone knows only
they have any worth compared to lowly humans with regular Star Seeds. (And with some genuine Sailor Senshi like the twins Lethe & Mnenosyne she instead convinces them that a being like Sailor Moon who was lucky enough to be born with the most powerful Star Seed in the universe is the
real source of all their problems and if they could just get rid of her, their unfair situation would resolve)
Despite the Cauldron having a clear system in place she refuses to be just a cog in it's machine and submitting to her fate, she attempts to take destiny into her own hands and take control of the very system that made her who she is. (and she's the one playing Chaos here rather than the other way around, who she also views as just another sad sack entity in the Cauldron's system) Galaxia's endless galactic genocide could also possibly seen as a revolt against the system, sure she's looking for the strongest Star Seed of the universe, a planet "worthy of her" but the fact that she seems to destroy every star that she comes across speaks to the sheer anger & grief buried deep down within her over the unfair situation she was born in and if all one's existence is determined by the quality of their Star Seed, then nothing matters,
life doesn't matter, so she should just burn down everything this twisted system begot. She seeks out Sailor Moon purely because she's the owner of the Universe's most powerful Star Seed/Sailor Crystal but ends up learning an important lesson regarding the value of one's soul & identity, human bonds and the acceptance of the circle of life despite it's unfair existence for some like her, but ultimately it's too late for her and to be redeemed she has to die which makes for one of the most poignant scenes in the entire manga up to that point.
Galaxia is the perfect SM villain in particular because she serves as the direct anti-Sailor Moon and does what a villain is supposed to do, challenge the hero's core beliefs and be an opposite reflection of themselves and their foil. Usagi, through Galaxia realizes she could've ended easily ended up just like her and it was only through sheer luck that she happened to be blessed with the Sailor Crystal Star Seed, Galaxia also helps Usagi come to an important realization within herself that fighting won't solve anything, that each and every star is in the same boat and that they're all ultimately the same, even Chaos, just lonely Stars beholden to a system that keeps the universe in balance, nobody is truly the villain in this story, this is just the way the world runs and the key to personal enlightenment is the acceptance of this fact all while making sure to treasure those fleeting, human moments in between, something Galaxia was unable to do and grew bitter as a result but that Usagi won't allow for herself.
Galaxia as a character & Manga Stars with it's core themes in general is a masterpiece in writing and the 90's anime in comparison can't even begin to come up to it's
shoelaces.
(still like to think she survived the fall somehow and just quit). Perhaps not necessarily more redemption but less death would be nice? Some villains could reasonably quit being villlains even without a purification. For example Kaolinite was content wtih just being Pr. Tomoe's secretary/housekeeper after her first death, and didn't care about being a death buster.
)
was a serious crime in my eyes. 
And yes, I very much enjoy the BMC too♡
