Pain does not have a reg debuff. It has a handy def and res debuff, but that is it. So yes, it does make it harder to solo difficult targets with this set. But look on the brightside, you can heal better than all other sets.
The Assault Bot has two moves with -Regen on them. Plasma Blast and Dual Plasma Blast.
And... Jounin have Poison Dart with -Regen on it.
I swore it did, but I checked Mids and I don't see any power with a -regen. Does this mean pain has a harder time against hard targets than other MM secondaries?