There are 2 factors in rams and catapults, one is attack power, that kills units, another is power of demolishing or destroying that destroys buildings.
both of this factors are affected by smithy.
Teutons catapult has less attack power. but ALL catapults (Roman, Teutons or Gauls) have same stats in destroying.
But if you go catapults, you can't get benefit from brewery. (unless you are going to destroy a village completely which aiming doesn't matter.)
If you go rams, first you have more base attack power, then you can (and should) party in brewery, which can boost your power significantly.
There are many successful reports of Teutons catapult hammer. It's as good as others is heavy hammers.
To be more clear
Romans in a day can make 334 Imperians and 227 EC and 71 Fire Catapults = ~90K ATTACK POWER and ~2K DEMOLISHING POWER
Teutons in a day can make 891 Clubs and 216 TK and 71 Catapults = ~95K ATTACK POWER and SAME ~2K DEMOLISHING POWER
According to kirilloid
Demolishing power of a level 0 catapult is 20 and at level 20, it's 30. (50% more power) and doesn't matter on tribe.