Newton's one-year contract has a maximum value of $7.5 million but is incentive-laden and is a "bare-minimum" deal, per Ian Rapoport of NFL Network.
Sherman's point regarding quarterback salaries is valid. There are 18 quarterbacks who are currently under contract for an average of more than $20 million per season, many of whom lack Newton's resume. Teddy Bridgewater, who is replacing Newton as the Panthers' starter, has made just six starts since the 2015 season and will make an average of $21 million in his new contract.
Most of the remaining 32 teams will enter 2020 with a quarterback on a rookie-scale contract, which allows teams to add depth at other positions. The Patriots were only in a position to sign Newton because most quarterback-needy teams recently drafted signal-callers.
The COVID-19 pandemic was also likely a factor. With Newton having undergone shoulder surgery in 2018 and foot surgery in 2019, teams were not able to have the quarterback in their facilities for a workout or physical, which could have depressed his value.
It's likely the Patriots' offer was the best Newton could get from an opportunity and salary standpoint, but Sherman has a point about lesser players getting more.