If Jaylen is actually upset and it's not just a short-term thing, then we need to trade him. I'm impressed that it's been kept mostly in house so far, but I'm sure the dam will break at some point if he's actually not happy. Brad said he had talked to Jaylen a lot. This probably means Jaylen has talked to Brad, as well. Maybe he is open to a fresh start.
I don't think overpaying him on an extension is a good idea. And making him captain over a clearly better teammate seems disrespectful. Even though Tatum has been the ultimate NBA personality, I'm sure he is over always hearing about FMVP Jaylen Brown.