I'm sure Ramona, who's (RIP Ramona) truly the reason Art was as successful as he was, really knew how to balance the bookings. That is an art that has been lost on all of these podcasts. The same people, over and over and over.
Most of those old, regular characters put onto a show today, it's tough. I think the interweb has pretty much killed the joy of discovery.
You said it. My favorite example was Steve Mahlzberg's producer, in that Mahlzberg was a bad m.c. but the parade of guests made the show listenable. The trouble is that that's a full time job, and I don't know these days who can afford to pay a staff of one or even several to be doing the research and legwork to line up guests. Man-hours to pay off in man-minutes of show.
The Internet has indeed made research so easy for us each to do for ourselves in competition with whomever they can pay. OTOH, it makes it feasible for us all to get leads on subjects we can then suggest to talk shows.