Japanese and English aren't the same language or accent. Maybe he still sounds different and it's just the same voice actor. If David would have voiced him in the game he still would have had to alter his voice to not sound like Solid Snake so I think the decision was a good one. It ultimately doesn't make sense for them to have the same voice for two different characters. Solidus was a perfect biological clone of Big Boss and doenst sound like Snake.
Also Idk if you finished MGSV but if you did then you would know why the protag doesn't sound like Big Boss in the game.
People need to let it go already. MGSV released and ended up being great despite Konami butchering the ending. They switched Big Boss's voice and the sky didn't fall. It's okay.
I still don't think he did and there's no evidence he did it maliciously while there is evidence that he changed it for the sake of continuity. It's happened in other franchises before.
So that's what I believe. Period.