I think it's fine the way it is:
While it's possible to build some kind of iron curtain with a mix of terraform, defence buildings, some units and cloak as support - it's still possible to tear down the curtain and let the sun come in.
If you takes the possibility away to let the sun shine, there will be a great chance of some kind of evoltionary development in huge team games, to fortify the front. So there will be either more 60-120 minute, instead of 20-60 minute games - or just less team games and everything is shiffting to 1v1, small teams - except some persons who like to play stronghold.
I totally understand the approach. But Zero K is a fast unit based game. And I can imagine a scenario for at least team games, where the gameplay is totally changing to tower defense. Besides I'm sure such a defensive fighting position can be exploided too, it won't be fun to be force to do this most of the time.