Not everything, only the stuff that humans do directly.
> One of the issues I do have with C++ is that you must use a really strict subset
The only reason is to avoid incomprehensibly complex code.
> (defeating the whole purpose of having such large standard library) in order to be reasonably sure your code will build and behave as you expect across different compiler/libstdc++ implementations.
That hasn't been true for ages. All modern STL implementations are reasonably compatible - you won't find problems with standard containers and algorithms.