I was just disappointed there wasn't more stuff about Queen Beryl and the Shitennou in the manga, like I was kinda led to believe.
I adore the manga but it's very true that fans hyped it up for years on the Internet before it was widely available. That hype consisted even after the manga was released, since here in the USA it was one of Tokyopop's earliest releases and the volumes soon went out of print. I feel bad for Sailor Moon newbies in general -- there is a LOT of misinformation and misleading stuff out there. Mostly things are better today, but there are still holdovers from the Internet of the late 90s. I feel like stuff like this is kind of related to what you're talking about.
Though, at the same time...there IS more about Queen Beryl and the Four Kings in the manga, though I guess the anime technically gives them more "screen time" (page time?) if you wanna go by that way of thinking. The 90s anime, if I recall, sorta-kinda hints at Beryl's backstory whereas it's slightly more visualized in the manga, and the Four Kings pop up later on in the manga but only for like a panel. So it depends on how you look at it.
Does Queen Beryl do more in the manga vs. what she does in the 90s anime? What about the Four Kings? Some would say that the Four Kings being Endymion's generals is really important and feel that not including that fact in the 90s anime automatically gives them more significance in the manga, but at the same time, they are definitely given more screen time and more prominent personalities in the 90s anime (for the most part).
I can understand being disappointed if you were led to believe that the villains accomplished more things in the manga or played larger roles, but at the end of the day, it's just seeing them in a different light.