I wonder what the extent of B&K's knowledge from Nuts & Bolts & Grunty's Revenge is.
I know that in Tooie, they have experience in FPS-like areas, but in those, the goals are typically to hunt down enemies that don't move much, such as the Clinkers or sticks of dynamite. They potentially have experience being a submarine that fought Lord Woo Fak Fak, a giant angler fish that shoots balls of electricity, & as themselves, fought Targitzan, but he's mostly stationary, beyond that he has rotating targets as his only vulnerable points & shoots darts in straight lines.
They did fight Grunty in that way, but Grunty was sticking out of her head & slinging spells, not doing much evading.
Mr. Patch does use projectiles, but doesn't move much & is a huge target.
There is a multiplayer mode -Which Heggy even references when Jinjo is unlocked for it in the main game- which has PvP FPS like combat.
So while they have plenty of experience with building & operating vehicles, hunting down many-numbered targets, they only have experience with someone like Doomslayer if we account for BT's multiplayer mode, & IDK if that's canon or not.
Plus, he may be a bit more jumpy. (B&K should be able to jump.)
(Gosh do I ever hate the Breegull Blaster.)
IDK if they have relevant experience against someone of Doomslayer's size, fighting style, level of mobility (However good or bad it may be.) & ranged weapon type battling.