Whether a fly is fancy or plain, complicated or simple, legendary or unknown - has little to do with it's effectiveness for catching fish. A simpler fly is not necessarily more effective, nor is it necessarily less effective. A mixed wing tied with 16 illegal feathers is not more or less effective either. A fly is effective if it is effective, period. There are much more important factors in catching steelhead than the fly itself.
Stating my case:
At any given moment, a wide variety of flies could catch a fish. But how many presentation styles would do it? Only a fraction compared to the flies that would work.
Then how many spots hold fish? If there is no fish then no presentation nor fly in the world can succeed. Does the angler know where to find fish?
If the rest of the angler's house is in order, then he or she can choose which of the flies from within the range of options to use as they please.
For some, myself included, the appropriateness of the fly design befits the species. For a wild steelhead in the cascade mountains, I would not be as pleased to catch a 20# native buck on a globug as I would on a big spring steelie wet fly with good swimming characteristics, even if they were both equally effective. Yes the mallard wings, the blue-eared pheasant spey hackles, the seal dubbing, a thing of beauty for both the angler and the fish to behold. A fly to be proud of in the photograph of the big fish's maw just before a gentle release.
That might not be the case for everyone, nor do I think it should - to each his/her own. But certainly for me I've reached a happy balance in a series of flies that are both aesthetically exciting as well as very effective for fishing, and have no reason to compromise. Life's too short for crappy flies