Is it that questionable when Barrie is going to get 8+ next season? Risto has 3 more years at 5.5, Russel got paid 4x4. For his offence alone his contract will probably be an underpay.
I know some will gag at this comment, but I try to follow the MacT model, you don't care how strong a player is offensively or defensively, the bottom line is does the player create more than they give up, the more often the player is on the positive side of that equation the better they are. There is room in the game for people who give up more than they create, but the second you accept that as fact you are dealing with a specialist for example a prime Boyd Gordon who bled goals against, but did so at a lower rate than almost anyone when given a steady diet of checking assignments and defensive zone starts or for example Sam Gagner who's not winning the 5 vs 5 fight all that often, but can potentially contribute enough on the PP to justify his spot on the team.
Ristolainen is definitely giving up more than he is creating so he falls into the specialist category, for me the most I'm generally willing to give a specialist even a high end one is roughly $3M, the unique thing about Ristolainen is he is still young enough that maybe he can break free from being a specialist into an outright solid contributor, but then you have to ask what is the probability of that occurring and how much of a premium are you willing to pay a specialist for the off chance that occurs.
Also with respect to Barrie he's been a net positive contributor for quite some time, not all offensive d-men who are defensively suspect are created equal. Most offensive d-men who are bad defensively get on the positive side of that equation by minimizing defensive zone time and increasing offensive zone time, Ristolainen conversely gets oodles of defensive zone time cause he is among the worst d-men in the league at preventing zone entries with possession and creating zone exits with possession. Ristolainen is the offensive d-man who is bad defensively who has a high probability of getting hemmed into his own zone and his +/- while not the best stat bares that out.