I think it's less a question of durability and more a question of long-term fastball effectiveness related to his release point. The less height, the less plane (which is crucial to FB effectiveness). A fastball released at 6 feet is considerably flatter and easier to track than a fastball released at 7 or 8 feet. You can dominate in college and the minors on sheer velo but major league hitters are far better at adjusting. Also, he may throw mid-90s, but the velocity is functionally less than a tall guy who throws mid-90s due to stride length, since the distance travelled to the plate is further the shorter the pitcher is. He will need to develop a viable 3rd pitch or he will get hammered on subsequent trips through the lineup. Luckily, his slider is a legit out pitch. I think he can be a starter but I don't think he'll go 6+ IP on a regular basis.