Just wanna point out that most of the things I mentioned advances your character in some way or offers some kind of progression, hence why people do them after reaching max level.
Also, given that everything can scale from lvl 1 to 30 in Anthem, it kinda means that any Stronghold will be able to serve as a lvl 30 stronghold, unlike something like Gnomeregan.
Anyway here's what the wowwiki lists as part of the endgame -
http://wowwiki.wikia.com/wiki/End-game
Covers everything from gear improvement, to rep grinds, leveling professions, pvp, achievement grinding
And here's the Guild Wars 2 wiki of "endgame" -
https://wiki.guildwars2.com/wiki/Endgame
Mention a host of things under different overarching categories
People do all kinds of stuff once the leveling process is complete. A large part of it is character gear progression for sure. But there's pretty much always things not related to direct power that also serves as a big part of the endgame experience for people. In Destiny 1 you had the ghosts to hunt for and the cosmetic rewards to get. In WoW you got people spending far more time grinding achievements, farming transmog fear, mounts, pets for pet battles than the handful or hours it takes them to do the raid each week.