Only up to the point at which we accept that the original character still persists. If a character's major development was done under a writer who didn't create them, then that second writer has as much claim on creation as the originator - not in law, necessarily (unless they're prepared to go to court and argue that their work was the major contribution to the concept), but certainly it's fair to say that, for example, Dan Abnett and Andy Lanning had more of a hand in "creating" Groot than Jack Kirby did. Groot is inarguably the product of Kirby's imagination (Marvel even credits as such), but Groot as a Guardian of the Galaxy (which neither man created) and Groot as inseparable partner of Rocket Raccoon (again, nothing to do with either writer) and so on is absolutely Abnett and Lanning. Without their input, the two characters (and various others) would still be languishing in obscurity; with their input, the two characters are a billion-dollar film franchise and part of the most successful wider franchise in movie history.
In the case of Groot there's so little there in Kirby's original - it's a by the numbers 1940s schlock thriller - that it's almost unreasonable to even give him the credit. It's certainly unreasonable to give him the credit for anything but the underlying concept (tree man) and the sole line of dialogue.
Similarly with Claremont vs. Hickman, there are innumerable things about the X-Men even today that were originated with Claremont. He was throwing everything to the wall and seeing what stuck. As we've seen with Guardians there's no particular barrier to a modern writer doing that - but Hickman hasn't. Arguing semantics about who created what de jure is not very helpful to understanding why Hickman fails.