What about the classical game where the aliens have one very good/lucky dretch and get s3 very fast?
Its hard to kill the enemy base when they have weapons far more powerful than you.
See, this is where strategy comes in. S1 can come back and beat S3. It's just highly improbable. But IF the aliens aren't coordinating, which may or may not be true because they owned to S3 so hard, groups of humans have chances of pulling something off, bit by bit. It's unlikely they will, but then again, you really won't see that kind of human coordination in a public game so long as people are so scared of tyrants.
Good builders divert the attacker's attention from the base structurers to the builder itself, so the base can nicely do it's damaging purpose.
Now that many servers have locational goon barb damage (headshots, body shots, leg shots for snipes), or in some servers, GREATLY reduced snipe damage, there is another use for humans--throw yourself in the way of snipes to save your base. Even at servers where that will hurt you a lot, it's better you die than you lose a turret. Doesn't take as long to respawn as it does to let a turret blow up or decon it and build a new one, in most cases. About two turrets is sometimes all it takes for a rant rush to come in and finish the job. However, if you know there's only that one sniper posing a threat, he should be dead in seconds.
Rants are not the initial major danger to your base unless you give them a clear initial opening. Snipers are, because they poke a hole in the seal on said opening, and give tyrants the opportunity they need to run on through.
