The question is who of Johnson or McCarthy is more likely to ruin Caleb Williams? Caleb is on his rookie deal. If the Bears don't win the Super Bowl in this timeframe, will making the playoffs be enough for him to re-sign? Who of these two has a better chance of getting to the SB? The one who has the experience and can get you into the playoffs consistently, or the high-upside rookie head coach that may need to be given a learning curve?
If I had my choice, I'd go for the risk reward hire. Caleb has potential to be elite and Ben Johnson might have that potential as well. If one or both flop, we can at least say we shot our shot.
McCarthy is a mid tier coach with some concerns. Caleb could still flop under him. Or Caleb excels and its the coaching holding us at a first round playoff exit team.
My nightmare scenario is the Bears end up like the Bengals currently. Elite level QB play and the franchise is treading water.