If you look at Johnson's highlights, he has very good offensive skills as well. So maybe there's a role for him on that side of the ball as well. Definitely a special athlete. Don't know why people dwell on his height. Average height for NFL corner is 5-11.
The reason you don't generally see 6-1 corners is that the laws of physics work against them -- they can't change direction fast enough to keep up with quick receivers.
Better to give up height on a jump ball than give up separation. Ask Wisconsin.