It's got a couple issues plaguing it right now:
-Its core rotation can't be expanded upon meaningfully. Cooldown weaponskills like Drill are inflexible without charges, but charges would take away MCH's only meaningful skill expression in how well you can keep to its static rotation.
-Machinist has 3 versions of Drill. None of them beyond the first add to MCH's gameplay outside of giving them enough battery to summon a robot at convenient fight times.
-It has a slew of mechanics that make it scale poorly with secondary stats. Hypercharge windows devalue skillspeed, Wildfire and Reassemble devalue crit and direct hit.
-They don't want to give Machinist itself any new, flashy high damaging attacks because of Reassemble. Reassemble is really boring and just paired with any cooldown weaponskill.
-Its capstone burst abilities, Wildfire and Automaton Queen, lack aesthetic impact. They're ogcd abilities that are easy to lose track of. Automaton Queen especially gets lost in the gaggle of melee and sfx, like, how often do you realize it even used Pile Bunker/Crowned Collider?
-Automaton Queen can't be controlled outside of its initial summon. It can end up attacking something you don't want to focus.
-Flamethrower is useless. It's kind of sad because I believe an attack like this could serve a purpose in a kit, like, if MCH really liked skillspeed and ended up with drifting issues, that's where you plug in Flamethrower, a resource neutral attack where you just torch stuff for as long as you need to realign your rotation with a burst window. However, it doesn't deal enough damage to have any purpose so it's basically worthless.
The devs already admitted that Machinist is "complete" as it is and can't really add much, so it's sort of at a dead end point. That's why the Automaton Queen ended up with MCH's highest potency attack that lacks any input. The only recourse is a rework.
On this note, I'd like to ask: Would you prefer Machinist's gameplay to be more calculating, or just APM heavy? The thing is, I feel like MCH could sort of double down on its hypercharge identity by become "the" APM based ranged class. Bard's main gameplay gimmick is paying attention to timers, Dancer's gimmick is having procs everywhere. I'd like for Machinist to be remain simple, but have a base weaponskill cast time reduction like MNK, SAM, or NIN to give it a more Trigger Happy feel.