1. C++ can do these things, and can do them quite performantly - but it takes an amount of effort far exceeding doing the same thing in say, Go or Java.
Not my observation, writing business servers in modern C++ using some libraries is a piece of cake. I do not have any problems with I/O and strings either.
This is a weakness that can be overcome, but it's a weakness.
I don't see having these things as separate libraries to be a weakness - this way they can evolve independently from the language and can be much more specialized.
To be sure, if you can accurately roadmap an application such that you can see how it's going to grow and expand across teams, then you can see where it makes sense to use frameworks to build areas, navigation, components, etc. and then be able to distribute work across teams.
But often very small applications with very small teams are built in a way that is unnecessarily complex, and the expected (later) payoff never arrives.