My archer brain is taking over, and I don't think we will see eye to eye on this because it's hard to explain where I'm coming from.
You are conflating equipment and form.
The "equipment" present in Eternal (bowstring, fletching, "plain" arrow) gives a slice of realism within the fantasy over the 90s, which I prefer. Her actual steps of shooting would be another thing. Yes, I did mention her elbow positioning is more accurate in Eternal, but again, that doesn't mean that I need her to have 100% accurate archery form.
With the Saint Seiya example, it's almost like you're saying "well, if you like it to be realistic then throw the baby with the bathwater away cause it's not as realistic as this." You're bringing in a whole other anime when I'm just talking Mars Flame Sniper.
The thing that you're missing here is that it's not supposed to be rooted in 'realism'.
If you want an anime about archery, it's Tsurune.
Despite supposedly the Flame Sniper taking origin from Rei's very obscure manga-exclusive archery skills, in the 90s anime it's meant as a fantasy take on firing a fire-imbued arrow.
It's not supposed to be realistic, it's supposed to be about the aesthetics - that's literally the whole stock footage, Rei looking badass with an arrow.
In the whole sequence of the 90s Fire Sniper, true to it's name, Rei takes more inspiration from as handling it as a sniper gun rather than a bow and arrow from the way she crouches, takes aim and moves the arrow.
The Eternal version, in turn, tries to copy part of it and I'll admit, it looks visually more appetizing at first, but in essence there's much less character acting going on than during the 90s version.
Sorry but a realistic bow and arrow doesn't sell it for me, it makes it dull.
What I'll commend though is the addition of a talisman tied to the arrow which if the sequence was a completely original one with perhaps focusing on the spiritual aspect of the bow and arrow, it could have been a really cool sequence.