Well it really depends on how many hours you play. If you clock 1-2hrs a day, I wouldn't be surprise if legendary takes a long time to drop eventhough you have high mf. I myself have been playing a long time, get tons of useless legendaries and only 1 set item so far.

But I'm not complaining. Coop with a friend and he had a 100m weapon drop while I've yet to sold anything about 10m.