Scenerios are really good for factions, and they're artficats and so many decks are running scenerios. Their granted cards gives you tempo and synergy which snowball effects are insane. People not playing only these cards, they're playing Caretaker with Scenerios. Which means playing only artifact removals doesn't help so much.
Yen Con is better than heatwave because it's a faction card and in every card game, faction,class etc. restricted cards to some other decks are better than neutral cards, if they have similar effects. And the Nilfgaard's principles depends on distrupt your opponent plays, for example Nilfgaard has spies which fills the opponent side of the board to get max value of the cards, Nilfgaard has so many lock options, opponent can't use their ability. Nilfgaard has Courier, Cantarella etc, to distrupt your opponent draws and use their ability for your purposes, bribery has the same ability, Viper Witchers also discards your opponent cards, Morvran ability actually has same principle, you are buffing your units against removal options etc. Yen Con has the same principle, to distrupt your opponent any play.
If opponent plays Yen Con with Calveit's ability, there is nothing you can do but for the other abilities, there is a solution. If you are playing any card which is really important for you, you could play defenders, yen con can't override the defender, Nilfgaard has to purify it before the yen con but you probably get good value from the card. If you haven't provision for that, you could play new expansions 4 provision card, idk the name but it must be Oliferi Merchant. It's ability is simple, swap your top card with your opponent top card, the card which be yen conned could be saved like that. That card is really solid, 4 points for 4 provision, 4 provision easily replaceable. If your opponent not a Nilfgaard, mulligan that card, if you still get that card, you could play that on round 3 for nothing.
I don't see any reason the nerf Yen Con. But about scenerios, maybe they could be beta CA spies, after their counter hits zero, can't be usable again. I mean using caretaker on them won't help the summon cards.