"James Gunn isn't the creator of Groot"
I mean sure, but does that mean that in the movies Peter isn't Ego's son because Gunn isn't their creator and Stan Lee, Jack Kirby, Steve Englehart, Steve Gann and Bob McLeod never intended for the two to be related? Does it mean Nebula isn't Thanos' adopted daughter but someone who claims to be his granddaughter in the movie, because that's how Roger Stern, John Buscema, Jim Starlin and Mike Friedrich thought about it?
I don't get this logic.
Even in the comics Groot's first appearance and his modern version have been retconned into distinct characters. Stan Lee, Jack Kirby and Dick Ayers never intended their "Monster from Planet X" to become how Groot is seen now. Keith Giffen intended his Groot to be the same creature as the classic "Monster from Planet X", but Jeff Loveness confirmed they were two distinct beings.
Of course the MCU version is going to be different from the comics, but it's kind of weird to act like Gunn has no say over the movie versions of these characters only because he didn't event their comic equivalents.