Yeah but observers like that wont be relevant in a very lowpop situation anywho, the main issue here is loosing the entire, or large parts of the hive, generally at lowpop to survs rushing the hive.
As for the post in whole, yeah i agree with chimera, just disallowing the survs from rushing the caves is a decent workaround, no one wants an early game end, but doing it OOC is a bit boring, and rules are hard to work with if not enforced as well.
IMO this feels like a mapping problem, just remove the guns/interest survs would have in getting anything there, and replace it all with IO stuff, its decently hard to push as marines, xenos cant melt it and survs dont give a shit about it.
Also, with the changes to capping you remove the evo restrictions on xenos, make the survs spawn together and give them actual limited class choices like how marines work, instead of being randomized which would lead to earlier fights and less rushing for gear. However thats still optional, IMO would play better.