My idea is simple: with a school is possible to upgrade walls to increase hitpoints!
There is much room for improvements in the walls available to Globs. Perhaps there could be weaker wooden walls as well as the stone walls. Both types with the capacity to be upgraded. Wood walls would be useful to create a defensive barrier when stone is not nearby - but even a fully upgraded wood wall should be no stronger than a level one stone wall.
I'd suggest that the level of a wall is decided by the build level of last worker to build, repair or upgrade it, so if you're building lots you don't have to go through and upgrade all of them one at a time.
Ah and more: If wall are upgraded are possible recovery hitpoints like a swarm but slow.