The Garviola sure isn't worth 2 population in it's current state, but you can't remove the pop cap on it either. If you remove the pop cap it allows players to make an unlimited amount of them.
In it's current state they are rather annoying then actually dealing some serious damage, sure you have to turn them on fire and make a fire in you're way to kill them, but on the other hand they dosen't kill units very fast so you can just run over them and completely ignore them.
If you are to remove the popcap you must instead make sure that you in some other way limit the amount of them you can make in you're base.
I do not think removing their popcap is the way to go, i think they need a rework to be more lethal though.