The fact that we're not rping with the original authors is actually the main difference imo. Because this is ultimately more of an ooc issue than an ic one.

If Eiichiro Oda wrote Luffy from One Piece as having stretchy limbs because he's secretly deeply insecure about his own stubby arms, it doesn't matter, because Jane from Accounting is the one RPing Luffy. There's a degree of separation that renders whatever "purpose" the character may have been created to fulfill meaningless.

You can actually see this in play sometimes, such as characters who exist in canon for almost entirely fanservice purposes, being fleshed out as their own characters through rp.

Of course, people can absolutely imprint their own issues onto canon characters too, so it's not even an issue unique to OCs.