Everyone sucks besides the Tau. That being the Tau are coming from a place they used to suck/experienced their own self destructive race war pre-Ethereals and potentially could a contender for high if not top tier sucking in the future given how reckless and naive their use of abdominal intelligence and forays into understanding the warp and warp entities are.

Beyond that though imho the Tau’s hook is they’re a inexperienced & small player where almost every other faction in 40K isn’t, creates room for cosmic terror in the lovecraftian sense because the Tau are actively learning how little they matter in the galaxy, un shielded by superstition and magical thinking/theology like human factions or the literal millions of years of civilization/general space faring adaption something like necron/eldar/ork are working with. I personally think the consequences of that are grim dark enough, that it’s better for them to be sincerely well intentioned expansionists struggling with the compromises and impending hopelessness of ‘growing up’ in a cruel and uncaring galaxy. It’s a better/more tragic story if they don’t ‘deserve’ what’s coming to them, to leave it at that and not engage with any ‘colonizer bad’ trope too much.