Players can absolutely improve, Fields included. Fields is also likely to continue to improve. The question is how much? Because if his deficiencies as a passer don't have major improvements, his ceiling is capped. To me, they don't seem likely to improve as much as is needed.
So now that we acknowledge that we're projecting with both Fields and Williams, the question becomes what are their projections?
IMO, and the opinion of most people that get paid to evaluate NFL talent, Williams projects to be a much better NFL QB than Fields. When you watch Caleb this is what you see:
- His quick release,
- His ability to adjust arm angles when needed
- Pocket presence/awareness with ability to maneuver in and out of the pocket
- Arm talent (arm strength combined with arm angles and ability to make every type of NFL throw with touch and accuracy)
- When improvising, an ability to make a quick decision and get the ball anywhere on the field from any platform
Williams is light years ahead of Fields in these areas. He projects to be top 5 in the NFL in those categories, and I think top 5 is conservative. This all jumps out of his game tape if you watch it with an open mind.
What will need to be answered is if Williams improves in other areas of his game to be one of the top 5 QBs overall, so that he's not just top 5 in those traits, but he becomes a top 5 QB overall. The only area that I can honestly give Fields a better projection is as a runner, but I would give a major edge to Williams in scrambling, since he is looking to pass as opposed to run when a play breaks down, and he's elite at that as well.