My brother plays MCH and he's been bouncing ideas off me as we progress in the fight. He (as he should) holds Raging Strikes for Blaster - when you should be getting a full RS+WF opener to burst the thing's ass off - and just uses Reload with Wildfire on Onslaughter alongside the shorter ogcds (read: all of them besides Ricochet) to drop a 5-6k Wildfire. Then he pulls off for the regulator with B4B+HE+Rapid Fire - gives mobility to dodge the laser if it targets him while making the thing die in like 5 gcds or so. He mentioned how he still has a few B4B+HE gcds left when he's back on the boss.

That's second-hand so a few things might be a bit off?

We talked about how he should try and open with 5 Ammo and then do the WF with maybe just 1-2 Quick Reloads and save Reload for the Steam Regulator but I dunno if that's a thing that would be better. He was consistently downing it with B4B+HE+Quick Reload with off-gcds.