> C++ is relatively fast but MSVC’s STL library’s debug performance is abysmal. It’s been like this since at least MSVC 2008 too. I’m not sure why Microsoft doesn’t think it’s a priority to improve.

If you want fast performance, you use a Release build. The purpose of a Debug build is that you can detect the source of as many bugs in your program as possible. So for Release build, it is a priority to improve performance (and in my opinion Microsoft did a good job). For the Debug build, it is a priority to improve the detectability of bugs in your program. Here also in my opinion Microsoft did a good job.