Do you understand that his snaps in practice are going to be limited, severely limited?
The collective bargaining agreement has cut out much of what was considered practice. Nowadays, there are very few contact days allowed, and, if you don't follow the rules, the head coach and the team pays substantial fines.
So the head coach does not want to throw away tens to hundreds of thousands of dollar, he has to give his QB1 some amount of live snaps. Do you seriously think that he is going to split the few live snaps allowed between two QBs in training camp? Fields might get some live snaps when the team is in shells.
Once the season starts, it is going to get worse. QB1 is going to take all of the limited snaps.
If it were the old time training camp with unlimited snaps, two or three training camp sessions per day, I could see even Foles getting a good share of snaps. In that situation, Fields could show great talent, some talent or a lot of work that would be required.
Now, it is get Dalton ready, if he is not good during the season, have Fields take his snaps the next week or wait until the bye week to give him some snaps. Try to figure out what you have with Fields once he is given a fair amount of snaps.
I guess that Nagy makes some plays specifically for Fields like Santa's Little Bazooka that Fields can run during the season.
I hope that Dalton can do well enough to keep the Bears in games, and Fields can show that he memorized the playbook so he can have a quick turnaround as the new starter if he is needed.