For endgame, it doesn't.
Repeat Neverreap/Fractal, or Seal Rock, ad nauseum for your tomestones, and clear Alexander each weak. Seal Rock is the only thing new here, if we're comparing to A Realm Reborn, but in a community that, for the most part, is purely PvE, that doesn't mean a lot... Heavensward is basically A Realm Reborn, minus the Relics, at this point... Although I'd honestly say it's worse than A Realm Reborn, because I find Alexander to be pretty lackluster, but that's what I get for going in hopeful, only to be met with nothing more than a pure DPS check... High Voltage wasn't much, but at least it was something, Coil was leagues ahead of Alexander off that alone IMO, never mind the story as well...
See, I agree with this, but... I don't think many people purchased Heavensward so they could do 2.x content, they purchased it for the new content... Had they expanded upon the old content though, by lets say adding a special Treasure Map to old loot tables, which grants access to a Guildhest-style Lv60 event (think BCNM style content from XI) for some relevant rewards, then we'd be talking... That would be something new, and it would be content that seems twice as filling, because you'd first have to beat Ifrit (Extreme) for an Inferno Map, before doing a special Lv60 instance against Amalj'aa for reasons.
Instead... Instead we just have Fractal and Neverreap... Going through old content duo/trio is fun and all, but it's not something I'm going to log on all week to do... Sky-Islands seem like the new exciting content, but that just makes the delay for 3.1 all the more painful... I got my fill of Amdapor Keep and Coil in the early weeks of 2.0, and I mean this in every sense, but that's essentially all Heavensward is offering right now... Well, were it not for Seal Rock, but I'm really not going to kid myself and pretend that's relevant for 90% of the playerbase. For most, Heavensward is either redoing Amdapor/Coil at Lv60, or redoing Amdapor/Coil in Neverreap/Alexander.