My primary takeaway from this thread is that if somebody works for years at a job, they get better at the job, which is fairly intuitive -- even Barker credits his experience hosting a local radio audience participation show for honing his skills prior to Truth or Consequences. Even the hosts that often get derided around here for their poor hosting abilities probably would have improved if their shows had lasted five years or so.
The only way a host gets worse at their job is if they've been doing it for so long, they've mentally checked out. Were there any hosts who got years and years of experience but didn't show improvement?