Tzeentch and Nurgle got pretty big releases, in one hit. Tzeentch got the Acolytes, the Tzaangor (technically were released as a 40k option earlier, but released again in their AoS version), the Tzaangor Shaman, the Tzaangor Enlightened, the Lord of Change, the Changeling, and the Gaunt Summoner and Ogroid Thaumaturge rereleased separately from Silver Tower. Maggotkin got the Great Unclean One, the Lord of Blights, the Pusgoyles, the Beast of Nurgle, 2 different heralds, the tree and the seperate release of Slimux. That’s on top of all the stuff Nurgle got in the End Times (where Slaanesh got nothing).
Slaanesh is getting the KoS, Daemon Prince guy, mirror thing, Masque and the scenery and spells. It’s noticeably smaller. Again, no one has been asking for a huge release here. Personally I’d have been happy for just one new unit. Hell, swap it for the mirror thing.