Carson's mechanics have gone to shit. He's regressed and when a veteran QB does that it's all mental. A really good example of that was Drew Brees in San Diego. He was playing like a deer in the headlights. And finally Drew was benched and they started Doug Flutie who changed Drew's career forever by personally taking him aside and talking to him. Flutie was honest and sympathetic and told him to clear his head of all the nonsense and to go outside the organization for help. He recommended a budding academy in Carlsbad. This was in 2004.
Flutie had watched on the sidelines as Brian Schottenheimer who was QB coach filled his head with nonsense and basically over-coached him. Schottenheimer was trying to totally change Drew's mechanics and how he read his progressions. What it did was make Drew try to think his way through each play instead of simply playing in his style that brought him success in college. Drew took the advice and began to blossom into the HOF QB he is today.
It was Brian Schottenheimer who pushed his father to play Drew against the orders of AJ Smith in a meaningless last game of the season in 2005 as Smith was working on extending Brees and he didn't want to risk injury. The rest is as they say is "history". Why do I bring up Brian Schottenheimer? Because as I watched Jimmy G play the last two years I see the same regression in his style of play. When he first came to SF he played as he was coached to in NE. He was steady, decisive, and accurate. Fast forward to the first game this year against AZ and he is a completely different player. He's indecisive and holds the ball too long as he tries to read the play the way Schottenheimer wants him to, and his mechanics have regressed since coming to SF and as a result, his accuracy has gone to shit.
Proof? Look at the film of his play that first season and look at his play in AZ a couple of weeks ago. When Jimmy G first got to SF he was on his way to being an elite QB. Now he's suffering from the same issues that Wentz is. Poor mechanics, poor reads, holding the ball too long, etc. IMO there is something going on behind the scenes in the Buff's organization, particularly in the coaching he's getting. That is normally the reason for this type of regression.
IMO that mental makeup and the type of coaching Goff is receiving in LA vs Wentz's mentality and coaching is the crucial difference. Wentz's game has always been making two reads and if it's not there to roll out and look for dropped coverages caused by the rollout or he simply ran. They apparently are trying to make him into a conventional pocket passer which he really isn't. Goff has always been a pocket passer and his rollouts are schemed as part of the play.
If they want to save him they need to sit him and allow him to clear his head. They need to carry him contractually for 2 more years and even then the dead cap will be over $12M for two years if they release him after the 2022 season. They may not need to sit him for a full season. A few games to clear his head, and most of all to simply change the scheme back allowing him to play as he always has when he was successful. If they do the Birds may revive this year and going into the future so this story may not be over.
The bottom line is that the fit between the HC and his offense is crucial to the success of the QB. Going back to Drew Brees as an example, Drew ran from SD, and the Schottenheimer's approach of trying to pigeon hole him into fitting Marty's scheme. What made Drew drop his moving to Miami was Payton telling Drew he would build an entire offense and scheme around him. On the flip side Marty Schottenheimer loved Philip Rivers because he knew from coaching him at the Senior Bowl he was a perfect fit for his offensive scheme.
I think Philly wanted to reduce Carson's injury exposure by converting him into a pocket passer. His injury history is testimony for the risk all teams take with the dual-threat QB. A pocket passer with good to elite accuracy is a far better prospect in that they have a much longer career trajectory. It's why the Rams made the right choice in Goff. They chose accuracy over mobility and it was the right choice.