Hainsey and Bellemore really didn't spend that much total PK time together on the ice...and Bellemore had significantly less PK time (total and per game) than the other 4. Most frequent pairings by far were Sekera-Faulk and Hainsey-Gleason. Not saying Bellemore was bad (or good), just that he wasn't used nearly as much so it's harder to make an apples to apples comparison.
I agree on the goalie(s) save% have a big impact on PK, but that isn't totally unrelated to the quality of chances the skaters in front of them are giving up. Any goalies SV% is likely to go down when you now have Rissanen, Liles and Murphy on the PK. The other impact of losing defensemen is it throws the pairings off. Guys develop synergy with their partner and allows them to react more quickly, knowing what their partner is likely to do. That goes away now. Hard to quantify that, but it is very real.
Anyhow, trading away 2 of your top 4 (TOI) PK defensemen is going to have an impact on the PK. It's not really much more complicated than that.