If you posit the idea that the game you linked, especially at the moment you linked it, tells us anything about the need for "base defense", then i fear you are grossly misreading both the game of izirayd vs googlefrog in question, and quite possibly the game of zero-k as well
What about crab spire as a response to badger? Or gauss popup can also outrange them.
Gauss works defensively and merely invites the opponent to tech up or stock up, in the knowledge that you've spent metal on a weapon that is not going to attack them anytime soon. Crab can work very well vs Rovers in general ime though, especially now that Dominatrix does not ignores its armor. Crab is the main reason i would avoid going Rovers on Ravaged.
That said, in this
situation, going Crab would have done nothing. GoogleFrog
had enough of a lead to switch to anything in response to a slow-onset 1600m move from izirayd
. Such as Tremor or even a Merlin.