If you're not as concerned about the tracking/privacy aspect of the unused Google launcher (or use DNS blocklists), you can keep the default launcher enabled and just intercept the home button to go the custom launcher.

That's what I always do and except on one cheap Hisense with a shitty built-in Google TV, there's no lag or stuttering and I see Projectivy immediately without ever triggering the default launcher (unless I want to open it for some reason).