I won't despute the nutters label, because they're clearly an
unhealthy religious cult, but I'm struggling to think of other instances where they've appeared incompetent.
I mean, it's more a profound lack of actual competence and efficiency, I guess, particularly tactically, which extends to include Mando himself sometimes. I mean this dude took the Darksaber into multiple fights, clearly without having even practiced with it (!!!), because he was hideously surprised by its weird-ass physics/inertia (it's clearly got something going on that lightsabers don't), managed to badly injure himself with it (frankly he was lucky not to lose a leg), and managed to almost-lose nearly every fight he's drawn it in, and in S2 (and especially Boba Fett, both his individual episode and the shared one) generally a lot of his tactics have been pretty much non-existent or just brute-force idiocy. Which is accidentally (?!) highlighted by people like Fennec Shand being extremely prepared and ninja. I mean, he's not Boba Fett levels of incompetent (#1227 in "phrases you thought you'd never type"), but it feels like S1 portrayed him as a Clint Eastwood-movie-level badass, who advised people pretty reasonably on tactics, but in S2 he was more of a "buffoon in cool armour with great reflexes/precision shooting" (a character surely familiar to many gaming tables!). I suspect S3 intends to continue the latter.
He was bizarrely good with his starfighter this episode, but it was the camera cuts causing his fighter to teleport to illogical positions (in at least one case I think impossible, as we'd have seen it on camera if it'd gone there), combined with the pirates using terrible tactics (they didn't even break when he was behind two of them, that's like literally the first thing you do!). The latter was at least partially explained by them trying to lead him to the battleship on their end though.
As for the rest of the cultists, I think there's more dysfunction than just "a buncha noobs" can explain (which I don't think is even the case given how many of them had multiple pieces of armour, something Mando took decades to get), esp. as we know some of them (like machinegun man) are more experienced. No-one took charge, no-one gave orders. Some people followed the leads of others, but it was completely disorganised idiocy and outright bad tactics. From that and the guy basically trying to mug him for the Darksaber it really feels like the cult has an "every man for himself" (in a sort of "ancient warrior" kind of way) thing going on, which is weird given they say the opposite.
But again, Favreau and Filoni, so can we know for sure they're meant to be competent or not? I think we can with the Darksaber stuff, but only because he was shown stumbling with it so many times and injuring himself.
It's particularly confusing because of Boba Fett too had a lot of just outright incompetence and it was unclear if that was intended as incompetence or just how Favreau likes it.