Having leveled the job to 80 now and tested various things, here's some feedback on the new machinist. Some of it is personal opinion, some of it design critique.
Hypercharge, Heat Blast, Gauss Round, Ricochet
The job can feel quite active and fun due to the massive amount of Heat Blasts and oGCDs you have to use. Or it can feel repetitive, spammy and stale. Personally, these abilities feel really weak and it's annoying to spam them all the time when you don't even see them making a big impact.
We avoided the worst ping nightmare when we couldn't fit 6 Heat Blasts into Hypercharge, but the job is still about as ping dependent as in Stormblood. The issue can somewhat be alleviated by spending all charges before entering Hypercharge, but that's not possible in all scenarios. It just feels bad to play when you keep clipping with Heat Blast and weaving oGCDs.
Drill and Air Anchor
These abilities feel powerful, but it's hard to track their cooldowns. The UI for their recast timers is hard to see in the middle of the battle and there's no clear indicator when they are ready compared to other GCDs so it's very easy to forget to use them.
Reassemble
The fact that this is a regular oGCD but has to be used on a GCD makes skill speed once again a somewhat useless stat for machinist. Adding filler GCDs and optimizing rotation for different skill speed is unintuitive and annoying because you have to delay your Drills on purpose to align them with this ability.
Wildfire
Wildfire suffers from the same skill speed misalignment as Reassemble though it can be better adjusted for a little better with the flexible Hypercharge windows. The skill feels like an afterthought now and doesn't really change how you do your regular rotation. You just tack it on to a Hypercharge window when it's ready and forget about it. Since you can land 6 GCDs into it's duration, it can be difficult for higher ping players to get the most out of it if any weaves during Hypercharge make them clip the GCD cycle.
Barrel Stabilizer
You would think that this can just be paired with Wildfire to guarantee having enough Heat for it, but doing so will actually make you overflow your Heat in a fight with full uptime. It's useful in situations with downtime to guarantee the Wildfire heat but optimizing its use can be quite unintuitive.
Automaton Queen
Another ability that feels like an afterthought. It doesn't matter when you use it because the potency per battery spent is the same. You just pop it and forget it. It has absolutely no effect on the rest of the rotation and you basically just want to exploit raid buffs with it. However, due to the long summoning animation and variable uptime, it's quite difficult to land it accurately within those windows.
Flamethrower
This ability is TOO WEAK. It's extremely difficult to tell if it's even worth using it at this point. It's barely stronger than Spread Shot but the fact that it doesn't generate heat means that it can very easily make you lose a Hypercharge window and make it a loss. This needs to be buffed to 150-200 potency to be a clear competitor to Auto Crossbow or it needs to generate heat so it can be used between Hypercharges as a Spread Shot replacement.
Auto Crossbow, Bioblaster
Fun AoEs, nothing to really say about them.
Overall
Machinist has become extremely flexible in some aspects but remained terribly rigid in others. It has a seemingly simple skill set but optimizing it is difficult and unintuitive. A lot of the abilities feel weak or detached from the rotation. Some people it might like the faster pacing but others will see it as too much work for too little gain. Ping problems have been very slightly alleviated, but ultimately remain about the same as before. Even if we ignore the actual dps losses, the job simply feels bad to play at high ping.