His problem is he lacks the raw pace that is needed in our mostly counter attacking play ,by the time he gets in the box the keeper has taken the goal kick
You say he is better than that (4th striker) then that he was on the bench to show the limitations of the squad ,he can't really be both . But as you point out his defensive contribution his his downfall ,he just doesn't look like a Glasner player .
On the other hand if he is not asked to track back and stay in an attacking position (say celtic) he would probably look half decent and attract the interest of some lower premier division team desperate for a goalscorer š