While I cannot hold a candle to Al as a guitarist, I would agree with classing the early Martin Carthy style as "Broonzy Thumb".   Latterly I think Carthy's guitar work has come come closer and ever to his dictum that folk music is in the time signature of 1. That would seem to distance it from US work.

All of it is a distance from whether an arrogant self-stated concertina player is competent to judge guitarists, and whether the benchmark is what he thinks, what the audience thinks, or what the performer intends.