He had 56% TS% and production-wise was equivalent to Towns. I would hardly say he had bad production. He is raw, that's not news, but I think he has all the tools to succeed big time in the league. If you are going to compare him to Portis, compare their freshman seasons. Here's PER40 numbers:
Portis is a more perimeter oriented defender, but is nowhere near the shotblocker/rim protector. Turner's also much better rebounder. BTW rim protection and rebounding are two of the things that translates best from college ball to the pros, I don't know why you have doubts it will translate.
BTW I also think Turner is better prospect when it comes to shooting. His form is much better and smooth, as evidenced by free throw %s. I think there is a very good chance he will turn into a great shooter in the league.
I love both as prospects, Portis is probably more of what we need right now as versatility in our front court, but Turner for me is the clearcut better prospect long-term.
BTW, what brings them really close to eachother for me is Portis' passing and playmaking... I have a thing for bigs who can pass and think it's an underrated quality.