Samberg's had 9 defensive partners with at least 60 minutes at 5v5 over the past 3 seasons (from most to least TOI): Pionk, Schmidt, DeMelo, Stanley, Schenn, Morrissey, Miller, Dillon and Capobianco. He has positive CF% with 7 of them, positive GF% with 6, and positive xGF% with 6.
Pionk's had 7 with 60+ TOI: Dillon, Samberg, Morrissey, Fleury, Stanley, Schmidt, and DeMelo. He has positive CF%, GF% and xGF% with 2 of them (Samberg and Morrissey).
Deployment probably has something to do with it. But Pionk needs to be carried and Samberg and Morrissey are the only ones who seem capable of it. Pionk struggles on the 2nd pair without a competent partner.
As long as Samberg sticks around and plays with Pionk, it's not a problem.