I never thought of Bobby as a singer so much as a shouter, dig. Exceptions abound, however; LLR, Sailor, and of course WRS. Funny thing I noticed a while back, my personal "imitation" of Bobby requires a little Elvis!
Now a good pondering might be comparing Pig and Brent, yeah? Such soul those two! And, to blaspheme slightly, I thought that Warren was channelling both of 'em.
Lots of people like Pig pen and i love his stuff and his time with the boys. but I think brent was a way better fit with the boys. well I think of all my favorite shows and they are in the brent era