Yeah, since the new provisions update ive seen less usurpers so thats something. I personally play a custom calveit with loads of disruption and deck control (redraws, summons, etc). I really want to try a Voorhis reveal deck, it looks really strong and so far around rank 23 i only saw one othet calveit. The rest were almost all Voorhis reveal decks and a few Emhyr witcher decks.
Emhyr is not bad especially when running a witcher deck. His ability allows for 2 uses of Vesemir mentor so you basically boost ALL your witchers in thr deck,hand and battlefield by 2.
People think hes bad because hes the default nilfgaard leader but he really is okay.
Ill agree though that nilfgaard isnt very popular, mostly because its not for everyone. Not the easiest but also far from hardest faction. Most popular factions i personally found to be in this order: Monsters, Northern Realms, Skellige/Scoia'tael(kind of on par, JUST below NR) and Nilfgaard last.
Lack of decent card combos or missing crucial cards means Nilfgaard cant have a wide variety of decks, so far i only noticed a handful of decks available, and i think this lack of flexibility and variety makes people unwilling to invest RP and scraps into this faction, although it can smash hard with the few decks it has.