I disagree with this.
Let's say the Chargers offered him a 4 year, $40M deal last offseason, with $20M guaranteed, which amounted to signing bonus and salaries in his first 2 seasons. Perhaps something like $8M signing bonus and salaries of $4M, $8M, $9M, $11M. If he signed that last year, he would have already completed year 1, and he would have already been paid $12M, with $8M to come in 2020.
Then the team could cut him after the 2020 season, and he would be free to go sign a new contract with new guaranteed money. Or the team could keep him and pay him $9M more. So either he would have made $20M and gotten more guaranteed money in 2021 from a new contract, or he would have earned $29M by 2021.
As things stand now, assuming the Chargers withheld all of the permissible fines from him last year and assuming he will get the full value of his new contract, he stands to make about $18.3M from 2019-2021.
I suppose YMMV, but I wouldn't call that "not much difference".