Yorick is a decent pick for mid... but not vs every mid.
He is best used:
- vs Slow moving champions
- vs Champions that depend on witting you down before they burst you
- vs Medium to short range champions
- vs mid-high cooldown champions.
- vs Skillshot reliant champions
- vs low sustain champs
Particularly I like Yorick mid vs the following:
It is not a long list, but yea there are a few champions that Yorick can counter in mid.