They are also varying degrees of batshit insane. Which, granted, jounin, but they were batshit even by the standards of the other jounin we see - I could totally see an argument that even as combat monsters individually, their combined effectiveness will be hampered even in comparison to a force made up of Kage who don't like each other. The latter will only betray each other if they think they can get away with it, and it won't screw their assault on Akatsuki - the confederation of S-rank nutjobs who (in canon, granted) only really work in pairs or alone and don't actually get along very well might crumble because Deidara thinks detonating his biggest bomb yet in a melee his "allies" are currently fighting in would be really cool, un.
This is going off of their canon personalities, sure, but if we take it as very roughly true that their degree of batshittery compared to other people we've seen in this quest is preserved, it might still be applicable.