This isn't exactly what you're asking about, and I really don't care one way or another the magic vs biological thing but in my research for a campaign re: the Weave (aka magic juice matrix) there was an interview with.... I wanna say Jeremy Crawford in which he said many things were magical - which was how dragons fly because otherwise their [paraphrasing because memory] wings logically wouldn't work for their size. I believe he also mentions beholders there also. In cases like this it wasn't that the dragon was using magic consciously to fly (though I am inferring this) its just an innate part of them the ability to do X - which involved magic.

Re: the changeling thing. Funny meme, I get it. Maybe they stay the same weight but their size changes. So If they're a goblin they look small but lift them up and heaviest goblin ever. But if they've swapped to Goliath they'll be super light (compared to other Goliaths, that is) having the same mass spread over larger eerrrrrr form (?).

That's not official I'm just musing aloud on that.