PythonVersionFromPath was meant to be used with the home path of python. So it checks whether python.exe exists in the same folder as the python??.dll. In QGIS is python.exe located in the same folder as the dll? And if there more than one dll's are located in the bin folder to which version python.exe corresponds to?

 // check if same platform
 try
 if {$IFDEF CPUX64}not {$ENDIF}IsEXEx64(DLLPath+'\python.exe') then Exit;
 except
 Exit;
 end;

As mentioned above PythonVersionFromPath was meant to be used with the home path of python and not with another path that just contains dlls and exes. Other PythonVersions functionality will not work (is_venv, is_virtualenv etc.). Also, your version PythonVersionFromPath is much slower than the original, since it uses FileExist for all possible python??.dll.

QGIS folder setup is a special case that you can accomodate in your own code.