I just returned after a long break, I always liked the idea of the Machinist when it first came out, but wasn't a fan of the RNG based gameplay on it's initial launch. Now I'm playing it again and enjoy the gameplay/aesthetics of the class, though I do have to agree that the base combo (1-2-3) needs a little expanding with separate finishers (as mentioned before).

Maybe instead of spreadshot/crossbow for aoe, the machinist (I don't know the lore/class prior to ffxiv, so forgive my ignorance on the class history) uses grenades (or something to that effect) for AOE, like a basic grenade (1) that does burst phys. aoe dmg, links into a firebomb that does fire aoe dot dmg (maybe low to med. potency but also places a +% dmg taken debuff on the target(s)), and use flamethrower as the heat gauge aoe burn.
Another MMO with a similar class (in style) is in Swtor, the Smuggler uses a hand held blaster, and grenades and it's a decently satisfying gameplay loop. I believe one cool gimmick the class had was throwing a sticky grenade that could be detonated by a follow up shot from the blaster. Could be interesting to have something along those lines somehow.

But I also agree that the role of the class should step away from any form of "support" role, bard and dancer have those pretty locked up, boost the dmg on MCH a lil bit to maybe compete a bit better vs the higher tiers.