I'd say this even if I wasn't a Brock Purdy fan: Josh Johnson is a terrible alternative.
He plays with zero urgency on those last few plays. If Purdy can't go I could see SF scoring zero points in this game.
That would be an interesting change in the narrative. If Purdy is just benefiting from the system and their offense gets shut down without him, what does that say? ( really only delusional haters are still on the "it's the system" train, though)