I'd argue that the entire point of using a shared open source kernel is that other users can benefit from additions.
Arguing "Who first added a feature" seems to be a losing spiral of needless tribalism. How many features does the Android kernel use that weren't developed by Google? Does that mean they wouldn't have developed those features? Or just that there's no point making a parallel implementation if there's already one existing.
The point here is not who first added the feature to Linux kernel. The point is Android cared about security, built a CFI implementation, started shipping it back in 2018, while Linux had other priorities and didn't have it until 2021. And even then almost nobody adopted it.
Arguing "Who first added a feature" seems to be a losing spiral of needless tribalism. How many features does the Android kernel use that weren't developed by Google? Does that mean they wouldn't have developed those features? Or just that there's no point making a parallel implementation if there's already one existing.