Arena, post season 5, began to become a poor indicator of skill because of the rampant boosting in season 7 and beyond and season 6 had such a poor population that I feel it couldn't have accurately depicted anybody's skill, players had trouble even getting rated.
In my estimation, to be considered good, you had to have had a top 1% somewhere on your record, preferably in an earlier season, but season 7 and beyond were beyond meaningless, which is why you can find players like you do.