This is true but if it's well known that you fire, say, 30% of your hires after 6 months then you'll have a much harder time attracting the kind of candidates y

This is true but if it's well known that you fire, say, 30% of your hires after 6 months then you'll have a much harder time attracting the kind of candidates you want to be attracting. You can compensate for the devs' opportunity cost with, well, compensation, but you'll be competing with FAANG, whose high-turn reputation isn't even 30% bad (with the possible exception of Netflix)