I think that the reason for reimplementing stl functionality is that they want complex types such as QString as a part of their external interface and they want different minor versions to be binary compatible which can't be guaranteed for types like std::string unless everything is compiled with the same compiler and runtime. See https://qt-project.org/wiki/Dpointer

As for the raw pointer use you should always use QPointer smart pointers for objects whose lifetime you don't control. However they don't recommend passing QPointers as function parameters since they are easily/cheaply constructed and the reference count is embedded in the QObject instance itself in any case.