It'd be a win for me, probably not for him. Or investors, sadly, at least not in the short term. I would turn off the non-Amazon sales platform. It might be feasible to save the brand, but of course the immediate effect would be a loss of that revenue stream from all the random Chinese "brands" that flood it with cheap garbage and counterfeits.
Or at least make a persistent toggle switch in the UI where you can say "I never want to see a single product that is not shipped-from-and-sold-by-Amazon." And end commingling with any product that Amazon itself sells, if that is occurring.
That's why they don't let morons like me run big business :). I care about things that only matter when you are a small business apparently.
Ah, focus on quality of products being listed. And, maybe that means there is room for a high-end competitor to Amazon eventually (am not seeing this anytime soon, but maybe in a couple decades??)