There's definitely reason to be concerned with Fields and he might not pan out, but unless you're drafting 1st overall and have a Lawrence or Luck in the draft, you're taking a risk. There's a lot to like about Fields and in a different draft he could certainly have gone 1st overall. QB is just such a valuable position that you take those risks with very high picks. Guys like Pitts, Chase, and Sewell have very few concerns about their transition to the NFL and yet guys like Wilson and Lance were taken above them, despite the alarming amount of weaknesses both have to work on. While you take into account the floor, you're really picking your QB based on their upside and Fields' upside is very very high.
My concern was paying the farm to move up for one of these guys. They might be talented players, but we would no longer have the draft capital to give them the necessary protection and weapons to properly develop. Giving up next years 1st isn't ideal, but you got to give up something to get something and we kept our 2nd and 3rd rounders these next 2 drafts which is enough if we scout correctly.
Also, let's not pretend like the Jets and Niners are necessarily smart when it comes to quarterbacks. Jets have a new regime, so it's unfair to pin past mistakes on them, but their ownership also does not have a history of hiring the right guys as of now. Niners are rather well run, but they definitely have made mistakes when it comes to quarterback. They gave up a 2nd rounder for Jimmy G who I do not consider to be good at all and then paid him a pretty big salary on top of it. They didn't have a choice, but it was still ultimately a poor decision. Furthermore, while being QB needy, they passed on both Watson and Mahomes to draft Solomon Thomas instead. I think Kyle Shanahan is a great coach for quarterbacks and find Lance intriguing and definitely think they can make it work, but it isn't as if Fields was passed up on by two franchises who are elite at identifying quarterbacks. Time will tell but a worthy gamble.