What if ground zeroes is actually venom in a coma having his memories altered to believe it was him there.
That's basically how I decided to think about PW in light of MGSV. It's just Venom's inaccurate version of what he thinks happened to BB during Peacewalker, so in my mind he just made up the garbage about rejecting The Boss as a way to give himself some motivations.
Though in the end, I think I'm just going to view both PW and MGSV as some kind of spin off/alternate timeline thing. Kojima clearly doesn't care about his canon, so why should I? MGS3/4 is where it ends in my head.