Wesley Johnson is below average in almost every statistical category.
His true shooting percentage is 48.6%; the average for his position is 53.7%. Below average from beyond the arc, from the free throw line, and everywhere else on the floor.
His PPS is 1.02; the average is 1.20.
He doesn't score much (15 points per 48 minutes, compared to the positional average of 20). He can't rebound (5.7 per 48 minutes, compared to the average 7.3). He's not a good passer (2.8 assists per 48 minutes, compared to the average 3.4). Fouls and steals are both below average, and he turns the ball over too much.
The only major statistical category in which he is NOT below average are blocks, and by a thin margin.
So, he's not a terrible player. There is just nothing he particularly excels at, and is below average at every other facet of the game.