He throws 100 MPH.
Velocity can be trained to an extent. Through improved mechanical efficiency and training, velocity can be improved for majority of amateur pitchers. However, you probably can't make 90 MPH pitcher hit 100 MPH. There is a ceiling there. Some pitcher just naturally can throw harder than others. Tyler Kolek is one of those guys.
He's a beast on the mound. He's a big bodied pitcher with a bulldog mentality. He knows he has an elite fastball and he will use it. You draft for upside, and a 100 MPH fastball brings a lot of upside.
Sure, his breaking ball isn't a plus pitch now, but there is a chance with his slider to be one. The curveball is behind the slider, and grades out as a potential above-average pitch. There is also a change up that is rarely used, since you know he throws 100 and two breaking balls.
He has pretty good mechanics. There are things to fix, but that's to be expected. He checks out with kinematic measurements. He obviously can generate momentum and force that goes up the chain efficiently. He has a large frame. He reportedly has a great work ethic which should alleviate concerns about him ending up with a bad body.
He's a high school pitcher and that caries a lot of risk. He could flame out. He could get injured. His stuff may not adapt to pro ball. He already shows control issues at times. What if that does improve?
All valid questions. But, the truth is you can say that about any pitcher.
If he's the pick, look at it very simply. He has the strongest arm in the draft. Something you can't teach.