In flex, I want guards who can shoot (Per/spd) and passing helps at all positions, because you can work a flex nicely with only 2 scorers - high passing maximizes your chances of finding them in the right spots. I tend to value speed over ath, also passing over ball-handling in the flex.
In the press, you also need speed, but ath and defense are very important, or you'll be in foul trouble. I think you're seeing that with Thornton. Ideally, I'd have a guy like Thornton come off the bench at multiple positions, so your opponent can't target him. If he's the #2 guy at both guard positions, and maybe even sf, he'll still see close to 20mpg, and may avoid foul trouble.
Speed helps at all positions in the press, but I value ath over spd for pf/c. Obviously, I'm trying to get the bulk of my rebounds there as well. I would be comfortable with Chandler at sf, as long as you have good rebounding bigs. Unless he's still blue in speed, he probably won't be fast enough to be a good flex guard.
If it's my team, and I'm trying to max success for this year, I would likely start:
pg - capra
sg - fields
sf - chandler
pf - barrett
c - rawls
I'd bring Thornton off the bench at #2 for pg/sg, have rutenberg set #2 at sf, and #3 at the guards. Roper is your #2 pf, schall your #2 c.
I'd be looking for about 20% offense each for Capra, Rawls, Thornton, and Rutenberg, 10% for Chandler, and the rest split among the other 4 guys. Right now, Chandler is more valuable to me as a distributor, maybe a 3rd option. That could change as the year progresses, he may end up a better scorer than Capra, so keep an eye on that.