FZ isn't in a slump because when I joined 1 year 1 month ago there was maybe 3 people on the forum a week, now it's 5 a day.
No one is getting paid making FZ, so it will come at a slow pace. GIMP took nearly a decade to get good from when I first used it in the 90s.
I was thinking that it might be a bit overly complicated, but when you think about it it's the complicated bit that makes it easy to actually use when you know the tricks.
If you ask me Inkscape is way harder to master than FZ, because with FZ you just have to make parts follow some rules.
I bet if someone did a full featured tutorial on FZ, and especially part making, with what everything does, it would certainly boost FZ.