The Crystal Gems are definitely awesome at helping each other improve, no doubt about that. I actually can't think of any trios that are better at it than they are. I only think some trios are better because I happen to like them more or I have been a fan of them much longer than I've watched Steven Universe. Trios like Ash, Misty and Brock from Pokémon, Harry, Ron and Hermione from Harry Potter and Huey, Dewey and Louie from Donald Duck comics will probably always be my favorites. There are many other trios from various cartoons and movies that I like as well, but none of them are better than the Crystal Gems.