I don't think this is a particularly accurate description of pytorch in 2021. Yeah, the original c++ backend came from torch, but I think most of that has been replaced. AFAIK, all the development of the c++ backend for pytorch over that last several years has been done as part of the pytorch project -it's not just python wrappers at this point.
What I like about PyTorch is that most of the functionality is actually available through the C++ API as well, which has 'beta API stability' as they call it. So, there are good bindings for some other languages as well. E.g., I have been using the Rust bindings in a larger project [1], and they have been awesome. A precursor to the project was implemented using Tensorflow, which was a world of pain.
Even things like mixed-precision training are fairly easy to do through the API.
