I'd keep them on board but I'd get rid of that backdoor and encourage them to adapt to the new situation, for a number of reasons:
- 'OldTubers' vs. the new Googlers is a clear us v. them thing. Bad for culture, especially when you get privileges on top.
- Their plan was actually successful so there must have been a thing or two to learn on the product side, even if it's as simple as accepting engineering input and understanding the difficulty of maintaining stuff (as opposed to relying on the analytics).
- There's some good thinking and ingenuity in there, despite the methodology.
I'd want to keep hold of that talent while dealing with burgeoning elitism. Up to them to quit if they don't like the changes. Fire them if their contribution begins to suffer.