User blog comment:Victory awaits/The actual outcome of Apocalypse?/@comment-26982641-20161001101547/@comment-1975828-20161001164232

I believe it's not all destiny, that Michael really needs his True Vessel in order to use his full powers. Had he used some random guy, Michael's essence alone would have destroyed him, even without using any powers.

Remember Hael? She wanted Castiel's vessel because it was strong and more suitable, not because of any personal preferences. She knew her own vessel wouldn't hold and if it couldn't hold her, it would not withstand her true powers either.

So yeah, I'm pretty certain Michael's victory relied on him possessing Dean, and if he had gotten to Dean before Lucifer got to Sam, then he would have an advantage. It's the same as bringing a broken sword to the battlefied. A strong sword works best for the user.