I disagree. You shouldn’t have to learn two debuggers just because you occasionally have to use a different OS. GDB has the right architecture here; the actual debugging operations are implemented by a gdbserver, and gdb is only the user interface that lets the user tell the server what to do. When you’re debugging on a different platform you use use a different gdbserver and keep using the same user interface that you are familiar with.

When you replay a recording, rr first starts its custom gdbserver (which reads from the recording instead of from a live process) then starts a gdb process that connects to it.

Why? From the user's pov, what 'low level integration with an OS' is there that couldn't/shouldn't be abstracted into 'generic debugging functionalities'?

I did use gdb recently on Windows, but this was for a cross compiled program using mingw. Not sure it works for programs made with MSVC.