I don't see how this would be easily spammible in future considering it has a high cost and the fact that other races would get techs that would take less turns to get and be can be made use of sooner. By the time orcs get this (which can't be sped up by workers) other races would have already had some siege units that can counter it easily. When the buildings get revamped (which would also result in a few campaigns needing to be revamped or removed) this would be averaged out with the other races. It's not like it has 10 range like humans ones do but since it's a suggestion for orcs I guess it's going to receive many more complaints from orc haters (

). Other races are catching up pretty quickly with orcs, one of which being the dwarves who are making good progress, humans are another one that's doing better. Elves are getting their but they are close and undead will be getting their soon enough from some of the suggestions I've seen, and hints. Scaledfolk, when we get the list expanded further and revamp the race, will start off slow but I don't think the race will take long to catch up because they are kinda like orcs in that they are easy to make units for and don't have a melee restriction like elves do.