In the OP's defense, people held the same belief with WoW's skill consolidation and look how that turned out. Seeing FFXIV borrows plenty of ideas from WoW, the OP's concerns aren't without some merit. Do I think we'll see something like Full Thrust combo become a single button? Hopefully not. That being said, some jobs will have to see some pruning. Even if you take away Piercing Talon, Keen Flurry and Feint, Dragoon still has a massive amount of buttons to its rotation. In fact, I don't even have Feint on my hotbar and still use 27 abilities. As I didn't count the aforementioned two or Elusive Jump since those are all situationally used, if at all, adding an additional five like they did in Heavensward would be cumbersome.
What I suspect could happen is combo ability are merged into one button-- with each changing based on proc duration. So True Thrust becomes Vorpal Thrust and then Full Thrust. Blade & Soul does this it, though I'm not entirely certain how I feel about it. While technically three different abilities, you are still pressing only a single button, albeit three times.