Personally, I think I could write a better screenplay than GR ... and I've never had anything published.
Frankly, I doubt it, and I say that without casting aspersions on your abilities.

Screenwriting is a very peculiar form. It looks deceptively easy. It isn't. You have to be able to write very economically because every page is a minute of screentime (45 seconds for TV), which means figuring out how little you can get away with to get tell the story. You really need to kill your darlings, and pare out anything unessential because every word is golden.
Then there's this very difficult trick of writing dialog which creates the illusion of natural conversation, but no one actually speaks with the precision that film characters do. Said dialog also has to sound right coming out of the mouth of an actor, which is something prose writers don't have to deal with.
Oh yeah, and then you have to accommodate all the production requirements (something which can be filmed under the budget) and also all the requests for tweaks to make roles more attractive to specific actors. I'm speaking from professional experience here.