He's not terrible. But how often does he take contested line outs? In order to do so you need to be quick into the air, strong in the air and safe in the hands. It's a skill that not all have, and not competing in the air regularly does not help develop it.
At Super Rugby level there's fewer strong competing jumpers so if they mark up on your best jumpers, you can go to a Skelton, a Palu or a Pocock knowing they won't contest, or if they do the lifter or jumper would need to move by which time you are already up taking the ball.
Get to international level and come up against SA where you have potentially Etzebeth (9), Van Der Merwe (6), Vermeulan (3), Whitely (6) or something similar who have all stolen ball this year, they can line up and rotate as jumpers or lifters marking up all your options. Then your only option is to go to the very back, which is the highest risk throw for not straight.