Really? Based on what? His stellar performance in a tie at home against the winless Lions, where he posted a 70.6 passer rating? Or was it the 35 yards on 8 attempts in mop-up duty against the Chiefs that gave you this impression? Anyway, it's not very smart to use extreme superlatives (like "best") when debating a point, now is it? Some assh*le tried to tell me that once. Oh, wait, that was you.
I'd say that Trey Lance, not Mason Rudolph, would be the overwhelming choice for the best backup quarterback by most rational NFL followers, if they had to choose.