I disable expa sion but also biters evolution. Without expansion and evolution biters are just the right amount of pressure for me for casual play without completely losing having to climb half of the game tech tree

For some reason I never had a problem with the biters on the default difficulty. I got the sense they were there as another ball to juggle rather than a primary antagonist. Simply building turrets around structures was enough to fend them off in the early game until I could proactively destroy their nests in the pollution zone. After I started doing that, they never bothered me again.