There are both great artists and writers. Sometimes their art is, great, good, okay art, but the writing sucks or the art sucks and the writing is great, good, okay, at times they both just suck. The artist does the art work and design, the writer makes the stories, character back stories, he writes.
When it comes down to creative control on picking powers for a character, who's job is that? who comes up with Super has these powers? it's a good idea or maybe he shouldn't have this/these power/powers?
He has the power to manipulate molecules. Should that be the writers decision or the authors because to decide whether to actually implement that.
I guess it all depends on like you said if the artist is good bad. But I think it requires both.
Because again to use the Sentry example when he stopped Thor's hammer.
Rick Remender must have wrote something in the scripts saying "As the hammer is thrown at Sentry he will proceed to stop it in his place with his telekinesis/molecular manipulation").
I think it requires the 2 to work together because the artist can't work without direction (unless he is given it).
I mean obviously it changes if the Author and Artist are the same guy but I think it requires too.
I agree that it takes both of them, one for creation then one for applying the powerset via art work, they must work together. Then there's the publisher like Marvel or DC that puts pressure on them because of the fans. So this is kinda a three way orgy, maybe rapeage from the publisher > writer/artist.