Well......according to this board, any extra $$$ at all is a raise no matter what the cap is, no matter what year. That's been the argument as to why the MVP and 2 time first team all-star RW are considered vastly overpaid (they aren't), even though they are at the top of their positions. (I agree with you on cap hit % as the measure of salary between players).
While I understand all of what you are saying - in this era, it's doubtful team is paying big money/cap hit for a player's going into his 14th season. Players know this now. Plus Matthews already has a rather significant injury history (Broken leg, shoulder surgery, wrist surgery), so it's not like he's an ironman.