Yeah, I've always found that the ammo finder perks are pretty underwhelming. While they're looking at armor, they should also buff masterwork armor. It currently does almost nothing.
Special is, I think, in a pretty good place. But Heavy? Heavy suffers from a strange RNG. There are times when I go through several battles and get nothing, then there are times when I get more purples than I could use in the whole strike from the first encounter. (I think Enhancement Cores are using the same RNG. I can get on a streak of gear dismantles that award Cores for a day and a half and then hit a dry spell the rest of the week.) The Heavyweight Heroic modifier has the same problem.