You just don't understand it. How is a cap increase "all" of the cap savings? You're the only one doing mental gymnastics.
Marner/Matthews/Tavares/etc. are already under contract and accounted for on the cap...Rielly is being given a raise with a new contract starting next year. Quite clearly the cap increases for next year would go towards offsetting raises for next year.
If you're talking about improving the roster (aka desperately finding something to criticize), then they can upgrade Kerfoot with the cap savings from his contract @3.5m + UFA Mikheyev's 1.7m. That's 5m+ for a wing upgrade like Domi, Smith, etc. or they can go a cheaper route on forward so to also give Campbell a raise (money from Kase, Engvall, Dermott, Holl, etc.).
Bottom line is that this contract is covered without touching the roster at all. If they want to improve elsewhere, there are a number of depth pieces they can move in order to sign a bigger fish.