When I think of drag, I think of theatricality. Someone can be a really good cross-dresser (not necessarily trans, but maybe that's part of the spectrum of trans) and be convincing and blend right in as the gender they're displaying. On the other hand, a drag queen or king to me, generally, is being over the top and attention-getting, which is completely appropriate if it's for entertainment purposes.
It seems one can even do "drag" within one's identified gender. I don't watch it regularly but I saw one episode of a show where drag queens act as guides for cis women looking to spice things up and maybe get a confidence boost. I only watched it because a friend's sister was in it. They had a "drag" competition involving make-up, outfits, putting on a show, etc. It was kinda cute.