I can't stand Coward but I think he is partly right. I made a post earlier in the year before Brock signed where I identified his positive traits and his deficiencies and what other teams he could potentially thrive with and the list wasn't that long. I think he can be a very good QB in the right situation. Is that worth over 50M a year. Probably not but the market is also the market, there are a bunch of non top 5 QBs that are getting "overpaid" and you need continuity at the QB position if you want to build a SB contender. This has been my debate with @BlokchainB who thinks you don't pay a non elite guy, but my position is you do pay a guy you know you can potentially win a SB with (they had the lead late in 4th and in OT in the SB against the best defense in the league with Brock as QB). There are only a few elite QBs and a few other young guys that have that potential. The chances of getting one aren't that high so do you perpetually suck cycling through QBs for a decade or more trying to hit on the next top 5 guy or do you lock up the guy you know you can win with, that your top 5 play calling coach trusts, for a number you know you can work with especially knowing the cap will likely continue to rise in the coming years.

As for Mac Jones, he is definitely underpaid. He is likely the best backup QB in the league. But he is underpaid because he wanted to come work with Shanahan to revive his career. If he does that, he will no longer be underpaid just like Darnold is no longer underpaid. I think the point "well you are paying Brock 53M and he is only a bit better than Mac Jones" is silly because you don't get to lock up Mac Jones playing at a high level for 5 or 6 years at 4M a year. So again what do you do, every year or two years you are going to try and find a QB whose career you can revive and pay him 5M and hope he works out and leaves to get paid 40-50M in the open market and you start again. That's fantasy football fan bullshit. Teams don't think or build that way.

Here is the biggest difference between Brock Purdy and Mac Jones and why they can win a SB with Purdy but likely not with Jones.

Week 1 Purdy was #1 in the league in sacks per pressure at 5.9%. Week 2 Jones was #32 in the league in sacks per pressure at 37.5%

If Mac Jones had played week 1 against a great Seahawks DLine and with Trent Williams and Ben Bartch banged up he would have been sacked 7 times based on the pressure rate and his sacks per pressure rate in week 2. The 49ers don't win that game if the QB gets sacked 7 times instead of once.