Fields's passer rating (and yes, passer rating is a junk stat) is now lower than his last years. His QBR (which factors in running and sacks) is 15 points lower than last season. Now - going by the eye test, I think he's playing significantly better than he did last season. But it's simply not good enough, for me, to sign him long term and pass on a top prospect at QB.
Anecdotally, he also seems helpless when neither Kmet and Moore are on the field. Now, he's got a bunch of schlubs to throw to beyond them, but the vast majority of starting quality QBs can at least do something with schlub WRs. Fields hasn't shown that.
It sucks because he's a good guy and he's still improving, but the circumstances are what they are. You got the 1st overall, you got a guy you have to make a decision on in the next few months. It's tragic, and there is of course the possibility it blows up in your face. There's no option where that isn't a possibility.