It's a possibility, since those abilities don't exist in the present class line up. I could imagine some of those abilities like Cutting Beam and Stun baton being a Tinker's abilities out of their mech (pilot abilities).
Looks good to me.
You would need to be in a mech in order to utilize heavy weaponry. It would be rather hard carrying around an arsenal of missiles and bombs in your knapsack.
Yeah, that's a cooldown to boost the already existing mech form. The actual mech form (which just consists of the clawback getting more armor and buzz saws for arms) is permanent.
Nah, that aspect would be altered to make it more balanced for WoW's class structure. They'd probably just make up some BS passive like "Mana Drive" that converts healing spells into energy that repairs the mech or some such silliness.
I have no idea why you think a Tinker inside a mech would be some invincible creature. You can still be defeated while piloting the mech. Look at Mekkatorque, Blackfuse and Thermaplugg.
Moonkin also gets a damage reduction buff. However that said, yeah it's a permanent form, and they even get Incarnation on top of it.
When its health reaches zero. And no, not 2 health bars. You can make it like Shaman Reincarnation ability, where they die and they can instantly rez themselves at 20% health. Do the same thing for the Tinker. Give the Tinker the option to eject from their mech before it explodes, and if they take it, they're at reduced health and can't eject again for 30 minutes.
Simple.
Maybe people didn't like your class concepts?