McCarron probably isn’t a 4C at 37, but 3.3 million will be nothing six years from now.
In 26-27, his contract will be 3% of the $104M cap. The cap will hit $123M in 28-29 and will likely rise even further by the end of his deal.
This deal will age well with the cap rising.
The only question here is will he be a functional 4C when he’s 37? If you can relatively unequivocally say yes, then it’s fine. Not great, but fine.