As someone whos favorite weapons in the game are shield weapons: Chaos Warriors having a mechanism that counters mindless shieldbashing is a good thing, though. Chaos Warriors have a cooldown / recovery phase after an attack. You have to time your bashes (and other attacks) to make sure you do them when they can’t sweep you. Letting yourself get whacked by one because you mistimed a bash is a mistake, not nescessarily an unfair mechanic.
I agree that - amongst other things - this sweep attack makes fighting a few CWs together or one in a dense horde hard, and sometimes pretty much impossible. The counter to that situation isn’t trying to out-tank the CWs / horde, however, but to try to pull them apart, and attack when you get an opening where you are not at rist from a sweep or punch. That positioning / maneuvering aspect is a very important part of the Vermintide gameplay! It’s not all just about weapons stats and skill, especially on higher difficulties. Also, there a plenty of videos of people demonstrating fighting several CWs, even with shields. They just don’t do that by trying to keep them all staggerlocked like a bunch of slaverats. Which is a good thing. Game would be quite stale otherwise.
The actual problems with the upswing sweep-attack are its too high damage value, uncomprehensible hitbox, and wonkyness where it sometimes seems to ignore blocks or survival skills. Its speed and unstaggerability, in my opinion, aren’t problems. Those are just factors that help make CWs interesting enemies, beyong just being damage sponges.