I am coming at this in another direction.
First of, what if you put a fly on a spinning outfit....aren't you now FLY FISHING, just like when you stick a worm on, you are BAIT FISHING (which can be done on a fly rod and reel.
I think the definition of FLY FISHING is what is on the end of the line, not the gear, but that is just me.
Plus, what is the definition of a FLY. Some say DRIES WITH WINGS, hense "FLY"
Others think the life cycle such a pupa, nymph, emerger, dry.
ALLOT don't think eggs, San Juan worms, woolly buggers, sculpin, etc. should be called a fly but rather a LURE which they are (and that is what the English refer to them as)

Anyway, MYSELF, I do use a fly rod, reel, LINES (meaning floating and sinking) and HAND TIED FLIES (which to me anything out of synthetics,hair, wings is a fly)
I made a commitment many years ago, that this was my ONLY choice. Kept my interest because now I had to learn "ENTOMOLOGY" and experiment with flies.

I have been fishing ponds where a friend uses a spinning outfit, with a bubble and a fly and he definitely out fished me with my floating line.

But, I find I am able to fish more ZONES with accuracy than other types of fishing. You are able to get to where the fish are and stay there, specially sub surface.

I am strictly ff, but I do believe I catch more fish, I very SELDOM walk away with the skunk smell and I have caught some of the BIGGEST fish, because I have a bigger choice of LURES and can get to the ZONE.

Long winded I know, sorry.