Hot Shot is Ability Bloat
First and Foremost:
I won't say that I am a machinist main, nor will I say it's 70 yet. I'm sure that (like so many other jobs) having access to your full kit makes a job feel complete, instead of a watered down husk that leaves much to be desired (pre 50 Dragoon). But one thing I have painfully noticed, especially since 4.0 is how entirely useless and redundant Hot Shot feels.
With the changes to Gauss Barrel, (increasing dmg output by 5%) It would have been no consequence to load the 5% dmg increase from Hot Shot onto it and eliminated the skill in it's entirety. Yes, the action generates "slightly" more heat than regular weapon skills, but is that really that significant of a reason? Really?
Furthermore, It feels awkward to use in most (all) cases, you don't want to use ammo on it, it doesn't generate heat if you do, and the extra 25 potency doesn't even really bother me. What this leaves you is a WS you want to use, but don't feel like wasting ammo on, so it forces you to consider using it before you even have ammo, or blowing a quick reload on it (which ideally is the best option available to you when you already have ammo)
Constantly needing to refresh it every 30 seconds is one thing too. Why does it matter? I know that DRG has a similar move in Heavy Thrust, and it's highly likely this was thought of in it's making. But that button doesn't really feel that good to press on DRG, either. Just another layer of complexity (that feels unfun and unoriginal) to keep up on.
That being said, Hot Shot Literally could have endless potential. It's effect could be changed entirely, it could be removed entirely for something else, there is so much this ability could be, instead of what it is.
It could be a DoT
Hot Shot sounds like it would burn. Why can't hot shot be the DoT WS that MCH lost? doing initial damage, and burning for over time damage? Great idea.
It could be a Buff
So MCH has this whole heat mechanic as of 4.0, it could buff or otherwise augment any one of the "heated" weapon skills that you use once your heat gauge is 50 or above, adding complexity that feels fun, and less generic. Split, Slug, or Clean shot could all push forth a completely different additional effect, depending on which one Hot shot was buffed to be used on.
It could be erased, and literally anything else could replace it
The possibilities are endless. Grenado shot back, Lead shot even. To be be honest Any variety of alternative AoE move would be stellar. Spread shot feels bad to use, and lining up the AoE feels weird in moments where you aren't sure if it's going to hit everything. Even bard has more than one AoE, one of which is on a CD much like Ricochet, but has a chance to be refreshed, like blood letter.
I feel like after MCH's opener, they are stuck pressing 1 until RNG prayer is heard
Hot Shot aside, (and it's replacement could be any number of fix to this) MCH feels like it runs out of steam very quickly. They do their opener, reload/hyper/combo/OGCDS, and then they're just... done. That was it, nothing to manage, nothing to prioritize, just. 1, 1, 1, maybe 2... While waiting for reload to refresh, and waiting for OCGDS to come back up.
I'm not entirely sure if this is intentional, but it's physical ranged equivalent feels constantly busy for much longer. I don't like comparing jobs, but SE seems to be hellbent on homogenizing similarly roled jobs as much as they can, instead of increasing their diversity into unique strengths/weaknesses for the sake of "balance," (it can't be unbalanced if it's the same thing)
Final thoughts:
I dunno. I want to like MCH. I want to give it a chance. But it's not even numbers that bug me. It's how it just doesn't feel like it's identity is fully realized. It's a collage of a couple of different ideas that seems hastily and hap-hazardly put together. It's like SE wanted to make the musketeer job the community demanded to have, but didn't want it to be just so. So they added a turret. But then... even that's where I lose them. What even is a machinist? This entire job feels like it's 3 expansions too early.
It should have been a garlemald job
Edit: I don't mean to say that Hot Shot should be removed, especially completely. (Title is somewhat misleading, forgive me) My point was to invoke creative thought on how this Action could feel more fun to use. To see others' ideas on how it could play more into Machinist's central kit. Thematically, it doesn't make sense for it to give a slight damage buff. Thematically, it generating heat makes more sense, but beyond this, it should feel more fun to use.