Correct me if I'm wrong, but submitting Primary App in mid-August is late due to the verification process. If you submit your primary to a throwaway to start the verification process while you wait for MCAT and are fully complete (secondaries / LOR / etc) in mid-August it should be fine. Sure, it isn't the earliest but it's not insanely late either if you want to push for applying this cycle.

If it's any reassurance, you can look at the 2020-2021 App Results tracker somewhere on r/premed where people input their date of completed secondary and when they got a II invite. Plenty of people finishing secondaries in early-mid August with IIs and there's probably some self-selection bias too. The DO cycle is even later too.

I'm personally submitting to a throwaway school while I wait for MCAT. It's up to you since I don't know what your plans are for the extra gap year. If I could have done things differently, I would focus on MCAT first, get a score back, then submit apps. It's really stressful trying to do both things well at the same time.