Lol. "He's pretty heavy". In 5th its size that matters. If its medium its fine. Even if it doesnt make sense, perfect swimming in plate doesn't either, but you dont just say to a player "oh btw in plate you die if you fall into water as you cant swim" while fighting around water for the first time.

Im glad you cleared it up after. In my case, I ended up leaving for other reasons but the nerf sticked. Mind you, if I knew at character creation it would be fine. But I didn't.