Thanks for the toilet tip, didn't think of it.
I remember those surv rounds where we started with 30-50 survs and marines deployed later. To be frank xenos lucked out. Most surv started with a stack of metal and at least half of them were not used. If they really wanted, we could hold that round for waaay longer.
I have 2 solutions for this, either make a separate game mode, call it extra-long round and do it that way. Make mats way cheaper so engis can build better, give xenos more larvas so marines can't rush them but slow down their evo dramatically so they won't have many high tier xenos. Slowly speed it up during the round. This will force a long round as neither side can push too hard with dorky T1s against 10 layer of cades and marines can't run in against 30 xenos.
Other solution is give back maturity that we had before. That would pretty much solve all problems. The longer the round goes, the most pressure and excitement marines will have and it will force xenos not to suicide, but play it slow so they can go ancient.