Beating it once does not prove anything at all. You do not become a pro from just one run. Same with crucible. People play all the time to improve and get better. They don't play and win one match and then say, "that's it I am good now and I don't need to play anymore because I won 1 match". No you have to keep playing in order to get better. I can't wait until hard mode comes out and you will be struggling more than before.