A combination of all of this.
Fields could be the greatest Taysom Hill the NFL has ever seen. I'd want to keep him to make the offense much more dynamic, but I certainly wouldn't want to keep him as my QB1. If I was an OC, I'd be excited to conjure a playbook that incorporates Fields' unique skillset. That said, I would NOT want to throw another rookie QB into an offense that has an abysmal offensive line and no offensive playmakers under a coaching staff that doesn't know how to properly develop or deploy players.
If they Bears draft Caleb and expect him to start right away, they'll ruin him too.