People don't get position and how you contribute is the reason Matthews got that contract. He's a C and scored more 5v5 goals than anybody which is the most valuable thing to do. It's worth more than 100 pt seasons.
Also look at this years RFA class in Point, Aho, Marner, Laine, Rantanen, Werenski, and others. Where does Marner even rank? I'd personally say #3 but somehow he'd make more than both Point and Aho who probably deserve more?
Naw, Marner is probably getting like 6x8.5. If Marner's surpasses Rantanen or Aho's the contract is an immediate bust. He'd have to be putting up 100 pt seasons every season to be worth it.