With all of the original people involved in Doctor Who gone, it was left to a soap opera creator to revive it. This was successful, and after he left, he turned it over to a guy he'd worked with before. Even though that guy had only worked on sitcoms and soaps, never scifi, he was clearly the one to make Doctor Who more scary. And thus began
Series 5Season 4.
Before that meeting, Gerry had been the guy who'd tried to make Corrie more fun and lighthearted; by the end of his discussion with Pedler, he was convinced that the world was doomed unless he could do something to warn us all. He never again wrote anything but sci-fi about either time travel or doom, except for one documentary about technological doom.
Most of the rest of his era's stories that weren't about Cybermen were about technology dooming the Earth or a future Earth colony, whether directly, or by awakening something dangerous, or by attracting the attention of Daleks or other aliens. After leaving the script editor job, he wrote one last story about Cybermen.
But The Doctor kept saving everyone, which ruined the point. So he left Doctor Who, taking Pedler with him, to create Doomwatch.
Gerry eventually followed Terry Nation out to America to become one of those once-successful British TV writers who can't get a break in Hollywood but won't give up, returning to Doctor Who a few times to submit new scripts about Cybermen, which were all rejected or rewritten to the point where his name was taken off except for Revenge, which was rewritten almost but not quite to the point where his name was taken off.
But in 1980, he had his big score with The Final Countdown, a movie about a modern Naval carrier time-traveling to 1941 and trying and failing to change history. This led to a decade of being one of those guys who gets a screenplay optioned every year but none of them ever get made, which means you make decent money but don't get invited to the cool parties.
In 1989, Davis and Nation tried to take over Doctor Who and retool it in a way that would be more popular in America (and with more Cybermen and Daleks, presumably), but the BBC decided they had better plans for the show. So Gerry returned to Hollywood and died instead.
In case you ever forget which aliens he helped invent, here's the list of his televised scripts:
And really, other than the first few stories (which he mostly inherited), most of Davis's run was pretty good, despite being saddled with the most forgettable companions of the early days until they finally introduced Jamie and then, at the end, Waterfield.
So, pretty good. Too bad you can't watch any of it.