I think he has great potential, was starting link up really well with Richi last season, before Richi got injured again, IIRC.
The biggest problem with Johnson is two fold and one has nothing to do with him.
His biggest problem is that he needs to grow a pair of balls and have the confidence to take his man on, even against slower players he rarely runs at his man and uses his speed, he is one of the fast players in the league. When the scums LB was on a yellow, Johnson should have run him ragged and he didn't and it was absolutely stupid not too.
Secondly, for some unknown reason, despite having some of the fastest players in the league, we play balls to feet rarely rarely utilising their speed. We miss so many runs by players down the line, just cut inside and pass the ball sideways and Son, is one of the worst for doing this, he would miss so many runs made by Udogie and others down the left, then cut inside and lose the ball.
You can argue that teams sit back though, and yeah, that is fair argument, then that case you play differnt types of players, players with more creativty and vision for a pass to open teams up.