Well, they aren't the easiest to break, but there are ways around them. Moltres and Delphox are two of the best responses as its STAB Hurricane runs through both of them handily. Virizion can easily come in on Momo to setup an SD on the switch to Amoonguss, and then SD again as Lum Berry gets her around sleep, but note that if Amoonguss has Clear Smog, this could pose some issues. Another way is Zoroark, particularly, a special attacking set that runs Dark Pulse / Night Daze and Flamethrower. This will easily cut through Momo while having Flamethrower to deal out serious damage to Amoonguss. It may not totally break the core, but it will put heavy hits on both ends of it to make it easier to break later.
As for the Venomoth ban in UU, I think it somewhat does have an impact here. (it definitely does in NU alpha, or whatever the hell they're calling it) Venomoth was one of those criminally underused Pokemon (much like Virizion) so it nips QuiverPass in the bud before people could catch on to how potent it could be. Obviously, a lot of the Grass-types will benefit from this as Venomoth would commonly use them as setup bait. Vivillon is now the only QD Pokemon worth using, so she can probably rise a little in usage. There may be some others I'm missing, but those are my initial impressions.