Being NBA ready has little to do with whether or where he would be drafted. Mason's physical gifts are fairly obvious and will be coveted by NBA teams.
I agree that his season so far doesn't scream "NBA lottery pick" but nothing about his performance negates his potential. One college season, or even three college seasons, is a relatively small sample size for an NBA player. Players' draft stock drops when they're exposed in some way - lack of quickness, bad hands, that kind of thing. Mason has struggled at times this year but he hasn't been exposed in that kind of way.