Then they just counter with "Yeah, but Shanahan is so good the recievers are wide open and any QB can make that throw." So essentially their argument is Shannahan is so good at his job he can take any QB and they will have HOF stats under him. Essentially he's the greatest coach in any sport ever. That's what their argument boils down to.
And that argument can be shot down by saying well, why didn't Trey Lance or Jimmy G work out? The doubters will respond by saying, they didn't have Christian McCaffery.
So in short, Purdy is only good because he has the best coach, best RB, best offensive talent etc. and all of that discounts how good he is.
It's a load of **** of course. None of those things work well unless Purdy is also great. You can draw up the best plays, but if you don't have a QB to change the play pre-snap, it won't matter. You can have the best WRs, but it won't matter unless the ball is thrown to them. And you can have the best RB, but if that's all you got teams can scheme and stop him. The QB is the lynchpin of all good offenses, that's why they (usually) get so much credit/flak when they're good/bad offenses.
And don't forget, for all of the talent that Purdy has around him, his offensive line is mediocre at best (outside of #71). That was the biggest thing I saw in the Eagles game. How freaking good would the be if they had the Eagles offensive line? Hurts has alllll day to throw (against a good niners pass rush).