Here's a thread
from April with some discussion on the subject. I've caught fish on wingless flies but I do think they can see the profile of the fly above the water. What gets one fish to hit a fly and another to turn away can be hard to parse, one might want the wing and the other sees something that is off.
That said, using grizzly tips on an adams rather than another feather or antron or calf tail, some of it is about following a pattern. Could be that patterns that have stood the test of time are the way they are for a reason, could also be that tradition trumps practicality. I tie flies to fish but I also enjoy working to learn a pattern even if it isn't all necessary.