Before the update, we'd rank for lots of long tail searches such as Black circular widget, usually number 1 for thousands of terms, but most are now pushed to the second page or not even ranking at all.
Based on what else you have told us in this thread, I'm going to guess that this, the Long Tail, is the real issue. I could easily be wrong, but I think there is some recent conversation about that. I'll look around and see if I can find it.
I have gone over and over and over competitors websites with a fine tooth comb.
Yeah, it's almost impossible to understand why pages that seem to scream out their violations of some standard or another get by unscathed and pages that seem to be at least inside the lines get nailed. .