I guess the main problem with siege engines besides the general distrust of them (something not working on a certain ver meaning they simply wont use that feature for the rest of their entire DF playing time in the future is a weird game culture) may be that you can't actually disern their attributes easily without risking them in active combat to learn it (not really possible from arena) which may yield dissapointment if they're not as good or effective as other alternatives.
I couldnt tell you its psi force of a catapult or a ballistae exactly, i know its in excess of usual projectile shooting weapons (maybe actually shorter than a blowgun) given the splattery messy effects that it takes to move a projectile through a armored opponent, but you get exactly the same psi force from "
minecart shotguns" which have become a aligned 3rd siege option with configurability of rollers.
Secondly, siege engines are barely moddable, so you can't actually learn very much about them like you can other objects in the files. If i wanted to build my own trebuchet for instance that had the variable movement of a ballistae shot (catapults have very little sway) but could fire down anything i put into it very hard fast & long i could apply foresight into building a correct range for a correct engine.
- I only know the actual length distances list by the extensive efforts of the wiki contributors passed on from forum researchers
Some people are also very competent at modding and could make a great use of expanded siege engine tags, like fired and unfired projectile states for things like setting alight brimstone ammunition without in-transit ignition (mixed results, often goopifies, easier to set the invaders on fire)