Been reading a lot on the forums and so far I have come to the conclusion that in terms of having it easy with less button mashing if you wanna:
Tank: P-Tech/Vanguard
Heal: Sorc/Sage
DPS: Sniper/GS
Scoundrel/OP healer sounded the easiest but they also have the hardest resource system to manage at least before I quit. Sniper is easy once you keybind cover to something you use a lot and get used to it. Commando/Merc might be easier but sniper seemed to flow better as they seemed to manage energy better than their Operative brothers. But I never played a Merc or Commando so just going by what I see at Noxxic for a rotation.
Because there's always a possible situation where you need this or that or this coupled with that. That's why they want more keybindings. In TOR, without macros, you don't need that many. In WoW, with macros, you can cover a myriad of possibilities. And like HK said, it's muscle memory. I thought that having to keep track of 10 keybinds was a lot back when I wasn't using macros. Amazingly once I moved to TOR, I learned to adjust to needing more keybinds and using them. It's all about adaptation.