By 2015, Picasa had excellent face recognition and Google Maps integration. XnView had none of that. Its "category" tagging was manual and clunky.
By 2015, XnView supported over 500 image formats (including 70+ read-only RAW formats from almost every camera manufacturer). It could open obscure formats from the 1990s (Amiga IFF, Atari IMG) that even Photoshop had abandoned. This was its #1 selling point. xnview review 2015