I have committed a great blasphemy in an act of heresy: I have added hand gunners to MOS as Gondor.
I have to tell you, though, that it is extremely satisfying to be able to shoot Mordor in the face, especially when they have Olog-Hai. The latter can be taken down by javelin-wielding marines of Pelargir and the axe throwers of Lossarnach, but those two units are rare and limited in their recruitment. I have made it so that virtually any large city and fortress can be able to recruit hand gunners, plus the custom huge cities and citadels of course.
Mind you, I see no need to add cannons of any kind, whether they be bombards, mortars, culverins or serpentines. The catapult and trebuchet artillery in the game are already overpowered enough. Walls are thus basically meaningless in TATW if they can all just be torn down that easily anyway, especially since the catapults have incredible range and usually great precision. That's especially the case when the AI commands it and not so much when it's your artillery acting like goobers needing to be court-martialed for being worthless drunks. On second thought, maybe I should add the cannons.