So, now that the Astra Militarium codex has come out, have you had a chance to see it in action? In two words: holy sheet.
I have a mate who runs 7(!) Leman Russes. He even ran them back in 7th because he's a self confessed treadhead. With the new rules he's essentially got 14 of the suckers on the battlefield, and although he only has two punishers... they are absolutely brutal.
I think pure Daemon armies are up against that proverbial wall on this army. While we have always struggled against armour imo, this just... hammers us. I think you basically have to be including Seekers or Nurglings to try and mask things.