Yeah I think Fields has all the physical tools and talent you could want, but he's a slow processer. At OSU he had a good OL and receivers, which helped him out as well as the level of competition. In the pros everything is faster, and the schemes are more complex.
I do think his processing improved this season, but it's still on the slow side. I don't think he gets thru his reads fast enough. You could help him out schematically but I don't Getsy went far enough there, plus they were lacking talent outside of DJ Moore and Cole Kmet for most of the season.
He's Vince Young ish.