Yeah.. making them hackable seems a good idea.. That is a cool way to get an advantage over the enemy.. But: if the enemy gets away with an artifact there is no way you will ever find him again if you have to hack it first.. making em hackable rules out any sort of mid-air fight..
I think it shouldnt be a traditional medieval catapult, but rather some sort of cannon with an entrance on the back... (and another player needed to fire the "projectile"/victim..

) And a lot of steam coming out when it fires..
Or the catapult could be aimable.. Some kind of control panel on the outside of the cannon to aim it to where you want to go.. Like a turret with human ammo

Maybe switching between set points, or only rotating left/right..
And that would give a solution to the hack problem too: Only the team that controls the steamcannon can aim it.. the other team can just use it to go wherever the other team has aimed it..