Why doesn't pve have pvp combo structure?

[Raikai]

You say consolidating buttons makes room for new skills, but then how long until you want those new skills consolidated and we're back where we started? After all, they all just deal damage.

You're completely ignoring the fact that the skills can do stuff like interaction, resource-management, etc. They can be something else than just an skill with a dps number to it.

About new skills being consolidated... It's inevitable. 3-4 expansions later, of course you'll have to revise everything and rearrange stuff to give room to more new stuff - That's exactly the premise of the OP. It's either that, or have your job never have anything new in future content. The way XIV leveling works is the same as WoW, you'll inevitably end with a bloat of unmanageable skills if you don't rework at some point. WoW though, lack severely at that because it "reinvents" itself with every xpac, and that's where the fault is.