My most effective flies, over the past four decades, have been the soft hackle GRHE (the rattier the better) and the McCafferty ant. Flies don't get a whole lot simpler. I think a lot of detail is mostly about showing off or boredom for those who really like to spend a lot of time at the vise. I've tied some realistic flies, just to see if I could, but I don't have any faith that they'd catch fish, and they certainly aren't worth the time and aggravation. If precise imitation were necessary for most situations, those molded rubber/plastic Burke's "flies" that used to be sold in tackle shops would still be widely available. When I see those now, they always look about ten years old, pinned to their yellowing cardboard displays.
-CC