The thing is that with 2 ranged weapons and a melee, Engineer can afford to take weapons that are more specialized. Me personally, alongside Gromil-plated, I also take Drakegun, Axe + Shield, and Piston Power (probably not the strongest talent in that row, but it’s so damn fun to use).
So with that kit:
Trash - Drakegun, also pushing with Axe+Shield to create space for it. I also do this weird thing where I jump around with the Drakegun, charging it in midair for short bursts when I land. Keeps me a little mobile in combat, and I find that little mobility helps reduce instances of that one jerk slaverat poking me in the back. Which, btw, is actually why I like Ammo Hoppers the least since it’s the horde clear option that keeps your back exposed for the longest. The slow ramp-up really encourages you to commit to long bursts, and I find as Engineer, it’s the one jerk slaverat behind me is what I take damage from the most.
SV and equivalents: Yeah, Gromil-plated tears these guys apart. Axe + Shield is also pretty decent against them.
Specials: Gromil-Plated vs. Regular Crank, Gromil is much better against Ratling Guns and Warpfire throwers, better at sniping leeches and sorcerers, but I think I’d prefer regular Crank against Assassins and Hookrats.
Beserkers: Regular Crank, particularly Linked Compression Chamber, is definitely a lot better here. If I get some generous distance I’ll use Gromil-plated, but often I find myself swapping to Axe + Shield, and moving to intercept so I can stagger lock them with pushing to protect thier target. I want to try push -> Piston Power next few times I face them to see how that goes, I’ve been mainly just spamming push since experience has taught me trying to sneak in attacks often ends in tragedy.
CWs: Gromil-plated isn’t amazing against CWs, but I’d still characterize it as effective and the existence of Grail Knights, Shades, and Bolt Staffs doesn’t change the fact that it’s effective. It stagger locks them with body-shots as long as they aren’t in an animation and take about half your ult bar to kill. Eh, shrug I’ll take it. I also use the concoction trait, and Gromil-Plated does much better with a potion on - normally being able to kill several in a patrol. Piston Power is really good against them though, but it sometimes gets me in trouble because I get too eager to use it.
Monsters: Crank’s better, but idk Gromil is still pretty decent, particularly with concoction. I think like a lot of Engineers I find myself pulling aggro pretty regularly, so I’m often just tanking it with Axe + Shield and knocking it around with Piston Power.
So that’s my kit and how Gromil-plated fits into it. Really for me, it comes down to the fact that I prefer Drakegun to the regular Crankgun, since I think Drakegun has more staying power (particularly with venting) , and is easier to use in a chaotic melee. Gromil-plated pairs better with Drakegun so that’s what I run.