PythonSlicer.exe inherits all launcher settings from Slicer.exe (as you can see it from additionalSettingsFilePath=/SlicerLauncherSettings.ini line in PythonSlicerLauncherSettings.ini), and it runs python-real.exe. Therefore, Slicer.exe --launch python-real.exe ...args... does exactly the same as PythonSlicer.exe ...args..., the only difference is that one is a console application, while the other is not.