To go back to the comparison at hand. Mays had a very high potential based on what he could do physically.
He fell because of what he could do physically, which is run in a straight line and hit hard.
Young went that high because he was a QB...An exceptionally athletic QB who had just carried his team to the NC....As in his potential was very much indicated by his on field play in college...the more people saw Mays play the more he got exposed...HUGE difference even ignoring that more exceptions will be made for QBs with potential than any other position...the only one that even come close to QB in that area is pass rusher, where teams will fall for size/speed pretty easily.
Again, Barron is a siiiiiiiiiignificantly better prospect than Mays once you get past Mays' 15 minutes of hype (which quite a few guys get during the draft process).