Lack of content doesn't really have that much to do with server choice. If anything, more bosses/content would make Epona worse, as older players may come back, and even more players may transfer over because Epona's distribution is "better".Add more content, Daily raids and new bosses for all level range, more like the cg weekly quest but for all level range and players get a chest reward with random items, add more endgame bosses with a stable spawn time, Epona is currently overpopulated adding more content like this will move players to move out to other servers, Vr doesn't waste anytime in banning accounts with suspicious activity idk why they can't do the same with making gameplay more attractive.
Players want to go to Epona because it keeps getting hyped up as "the best server"....whether that's true or not is simply a personal opinion. Yes, it's one of (if not the only server) that uses mostly-random drop distribution (which I feel should be in the game anyways, but that's a different topic), but that's because no other players really want it enough to work to change their own server. If players were to start redirecting to some other "dead" server with the goal of turning it into another Epona, it might start to lessen the load on Epona a bit. The problem there is that it's really hard to lead the charge of change, and is much easier to tag along with something that already exists.
Epona is overpopulated definitely, but from what I've seen it's only partly because of the drop system - I'd say another large part of the reason is because of all the hype that people generate for it. It almost seems to fit with the chest mentality - you can either work hard for items by a ton of farming/grinding, collecting DKP to eventually spend on loot...or you can spend your time going to boss after boss (still grinding/farming) and hope that you eventually get lucky in rolls. Both scenarios appeal to different people in different ways.
It would be nice to see VR working towards ways to expand server load for large numbers of players (that was a main reason behind the global witch boss over the Samhain event). However, there isn't really any way for players to know if that's possible/likely to happen.