on what basis is kat bad ?
While a katy can wipe just like any other rocket arty, its barrage is spread out over a longer period of time compared to other rocket arty, giving the enemy more time to retreat. Unless RNG favors you or you are close to the barrage target, the German player can afford to wait till after the first salvo before deciding if retreat is in order.
It isn't bad per say but it has a lot of negative aspects such as what I mentioned and having a larger hitbox than other rocket arty platforms. It doesn't even have a token defensive weapon unlike its German counterparts. Also, its special ability just gives even more time to react.