Not so. $ per year does matter because it affects the yearly cap.

Yes $ per year matters because it determines what is deducted from the available cap space.
If someone gives Cousins $30 mil (and they will) that is an enormous cap hit immediately. And it absolutely puts a huge dent that team's ability to keep or acquire other players.

Guarantees essentially determine the effective length of the contract as well as minimum overall value for the player and cost to the team.