They're not terrible.
Hmm, variety, that sucks. Uh, I mean, great! An efficiency dilema! You have 4 opponents with good saves (Marines,
Aspect Eldar, Necrons, and Tau). You need weapons that defeat these. You've got choices ta make.
Power klaws help, burnas help (in close combat), in a Kos you have few options that give you armor save negation.
You could go the "more-dice/more-potential-wounds/more-likely-they-fail-armor-saves route with lots of big shootas.
But you also have 'nid and IG foes. Skorchas for infantry. Burnas for infantry. Big shootas for infantry. Lobbas and kannons
on guntrukks for infantry. Rokkits, twin-rokkits on vehicles, burnas, zzap gunz, tankbusta bomz, kustom mega-blastas for
tanks and transports.