Söder understands the difference between electoral rhetoric and Realpolitik and so do CSU voters. And theatrics. He can go “I’ll keep an eye on those breaknecks, make sure they don’t convince the CDU of anything stupid”, occasionally make noise, and keep it at that.

The “main enemy” thing is absolutely true, of course, just have a look over the border to BW. But that’s about state, not federal, politics, and as long as the CSU keeps ruling Bavaria they’re happy.