No, the “whole” of PlatformIO would be in C:\Users\<user>\.platformio, it’s “just” deleting the PlatformIO package from the virtual enviornment created with the penv folder therein.
However, it seems then that you have multiple cores installed? The one in .platformio is at 6.0.2. And the 6.0.3rc1 core is where? System-wide? When you open a new regular terminal outside of PlatformIO (Cmd+R → cmd.exe), does pip uninstall platformio try to uninstall a different PlatformIO installation?