So with the way power creep has been, a lot of ESOs content has been getting easier for top end players, and now with the addition of subclassing, that will be even more of the case. For example, I just watched a video of a top tier player completing Vet Hardmode March of Sacrifices entirely solo. For me personally, I think that things like that are fun, people thinking of ways to be as strong as possible and the power fantasy of being that strong and knowing that you can achieve that appeals to myself and some players.
Instead of nerfing everything (which often just rubs people the wrong way), what if ZOS just leaned into it? By that I mean, what if they added achievements, like titles and a scoreboards for people that completed Vet content Trio/Duo/Solo. They would add hundreds of hours of gameplay to the game for top tier players, without actually having to create much of anything. Just leaderboards and titles. They could add more rewards, but I think locking rewards behind feats this difficult could rub a lot of the more casual players the wrong way, so it'd have to be handled with care.