I really like his improvement from last year to this year. I really think he will keep getting better and be a #1/2 type starter. He has surpassed my expectations this year.
to your point, it would make sense, but I am sure there are some obscure stat that shows slower pitchers get hit harder.
Depends on the guy. I bring up Brad Radke periodically in here as a guy who had awesome command but gave up a ton of HRs (especially early in his career) because he was always around the plate and didn't have overpowering stuff. I know it's a generalization, but usually hard throwers are at the top of the strike zone and command guys are low in the strike zone. Bill James did some interesting analysis way back when about how ground ball pitchers can get tattooed when their pitches are up a little, so it's not like command makes a guy immune to the long ball. I think Foltynewicz' problem is that he can't put guys away and he ends up aiming the ball.
The thing I've noticed with Folty is that his command and confidence in his off-speed stuff varies a lot from game to game. When he's got it going hitters can't sit on the fastball. He gets into trouble during games when he goes to the fastball whenever he gets into a hitters count.
What I noticed in the Giants game is utilization of the changeup. If he can throw it for strikes and keep the same arm action, that's his key pitch IMO.