The problem with 25 mans was the normalized gear (as you say) as well as the extreme homogenization of classes. At that point, it's not necessary, interesting, or even fun to gather 25 trusted or experienced people to face a possibly more difficult challenge than to go into 10 mans. Insert vanilla reference and call it nostalgia or fanboyism all you want, I just think the vanilla model of having several different raid sizes for different goals was the better model. UBRS was a gearing dungeon/small raid that, for the most part, was played with 10-15 players depending on the time of vanilla, ZG was a later 20 man raid helpful to both newer raiders and experienced raiders in gearing up for the more gear-intensive 40 mans. They all played their part, but the most important thing is that they all got played.
Having all raids be equal and available as 10/25 man just makes raiding a little bit more boring, uninspired, and less-rewarding.