Slightly safer for Monken and that is based on his resume alone.
Johnson took over a multiple pro bowl QB and polished him up slightly. Monken has been the OC for completely different skillsets in his QBs with Jameis Winston, Ryan Fitzpatrick, Baker Mayfield, and Lamar Jackson, He has also been a HC for S Miss.
I like BJ, but Goff and CW are completely different in their skillsets, Can BJ adapt to the different skills and weaknesses of CW? hope so, but Monken has a resume of actually doing that. Can BJ handle being a HC? hope so, but Monken has experience (college level) of actually doing it.
On paper Monken looks way better. But you are correct there might be something with his personality that teams have kept away from him. who knows, but on paper he is the safer option. Time will tell