I am not ignoring or adding to the code. In my opinion, the attachment of a lug to the thin metal of an enclosure like a panel box cannot be made securly enough to provide a low impedance grounding path. In my small area of jurisdiction, my opinion counts to the degree as already discussed. In another inspector's opinion this grounding method may be OK, I don't know. I could have my opinion changed by evidence to the contrary, but I don't see such evidence presented here, only opinions.
I will say this: I have approved using grounding clamps to building steel (a much thicker metal) by using the method you have described. Threaded holes (with at least two complete threads) or bored holes using corrosion resistant bolts with locknuts are OK with me, so long as the paint is removed, and the metal is protected from corrosion afterwards.
