But everyone has their own subset that they want to use, so I still have to know and understand it all if I want to read other people's code. And moreso if I want to do anything with that code.

This is largely an issue with C++.

Code in other mainstream languages remains generally readable even if the coding style changes.

I was indeed thinking of C++.

I personally believe in this too, and feel the same way about frameworks too. Other dev's have the "use every possible feature so this can never be removed" mindset which his bit me in the ass repeatedly.