My own thoughts on why Brownie McGhee is not given his due recognition is that "familiarity breeds contempt" Terry and McGhee were a great duo and both amazing musicians. They toured widely and and made numerous recordings their music therefore was readily available and perhaps too familiar. It's the old story, if they had only ever made a couple of sides we would be saying about how great they were and wouldn't it be wonderful if they had recorded more.
Fortunately Brownie lived reasonably comfortably to a reasonable age.
No tragic early death or fictitious legends and praise from expert pop musicians who never met him to tell us how wonderful he was.

He was a great picker and singer. As to which styles are "undervalued" Delta, Piedmont, Texas ? it's all a matter of personal taste.

Vic, I too saw Lonnie Johnson a couple of times. Unfortunately he was more into ballads when he came over like his King recordings using electric guitar. Personaly I would have preferred to hear him playing some of that old acoustic style that he did on a twelve string. However like Josh White he was playing what he thought his new audience wanted to hear.