OU did a Swift Swim + Drizzle ban, while not all of the sweepers were broken ('karp, 'disc in particular)
Drizzle + Swift Swim was a pretty big mistake IMO. Imagine you were on a ship and it's taking on water (no pun with drizzle). You see there's one hole on the deck that's shooting water, so you figure Ah, this must be the cause of the sink shipping! Yet, you fail to realize that water is actually just pouring over the sides of the boat...
Drizzle + Swift Swim was only a symptom for the real problem; Drizzle itself. Nobody wanted to say Drizzle was broken and thus get rid of it since it opened up styles. The one style that truly put me over the edge and made me leave OU for good was HO Rain teams in the early BW2 era. Politoed/Torn-T/Genesect/Keldeo were too much. Drizzle was the main problem, not Drizzle +SS, although that was one of the easiest strategies to abuse.
Complex bans don't work, they only fix one symptom, but don't handle the underlying cause. If you took Drizzle away from Politoed, it's pretty bad. But, Venomoth is a special case. You can run Tinted Lens > Wonderskin and it has a good chance of getting it's job done of QuiverPassing. So, if Venomoth is to get banned, it'll be because the accumulation of traits in Sleep Powder and QuiverPass, which is unique to Venomoth and Smeargle, not because of one ability in Wonderskin.