nitrof:
I tried to put some #pragma message into those define, And I got only the one I was expecting.
Maybe because you messed up:
nitrof:
#elif defined W5500_H_INCLUDED
#include "Ethernet2.h"
#pragma message ( "W5100 network" )
Note that the libraries are cached after the first successful compilation so after that you need to change the Tools > Board selection to clear the cache to get warnings from the library again.