Could never really work out JNT, as his reign was during the show's long decline, and I know Tom Baker didn't like him. However, he did last for almost ten years on the show and made it into a big export for the BBC.
Tom Baker didn't like Graham Williams much either, and I would argue the decline truly started during the Williams panto era. If anything, JNT arrested the decline, for a while anyway. I doubt the show would have lasted another ten years if Graham Williams had been running it.