Even if you don't use/have paladin weapons, catapults are worth it. Especially if you're under heavy attack and still haven't maxed out your farm populations (or you got cleared). They're just that more defensive boost.
If you think about it in real life (well....many, many years ago) - a catapult was used to sling large boulders into attacking troops cutting huge paths through them if they were bunched together.
the thing about cats being useful in TW, is that if you run a SP/HC build. when you are truly in need of troops you can also cue Cats while the Barracks and stables are already at work.
Aye, even if you don't run a spear/HC build, switching to one when in a war and under heavy attack whenever a defensive nuke gets cleared, is a good idea. Building cats to go along with it is even better.