I've done my homework on this. You did say qb rating or quarterback rating or QBR.
Tannehills last 3 QBRs in Miami were : 45.6, 48.6 and 33.2 Ryan Tannehill Stats | ESPN
Darold's QBRs in NY were: 45.9, 45.6 and 40.1 Sam Darnold Stats | ESPN
Even ESPN, the owner of QBR, calculated the multi year performance of Tannehill vs Darnold
Tannehill for whatever reason (injury, coaching, whatever) was not an average quarterback and was traded for a 4th and change. The Miami Dolphins, the NFL QB market and ESPN did not view Tannehill as an average starter.
His QBR was 32nd at the time of his trade. He passed for less than 2000 yards.
I will never understand the love some Panthers have for Tannehill's time in Miami.