Whether Josh has a higher ceiling than Cam is irrelevant. There are two relevant questions here:
1. Is JA's ceiling higher than Rosen? That was the choice in the draft. People seem to forget Darnold and Mayfield were already gone.
2. Is JA's ceiling higher than other QBs available in the 2019 draft when we pick in the top 5?
I guess you could add Mahomes in there, but Beane wasn't even here yet, and we don't know how much say McD had in that draft. And anyway, 10 other teams passed on Mahomes, including the Bears at #2 who took Trubisky as their franchise QB, and the Titans, who moved UP to take Corey Davis but left Mahomes on the table.