Yeah I mean I have the Stainless steel block mods, and had 3-4 layers of stainless steel, playing with a friend on insane. On that difficulty it least it doesn't matter what you have, they tear through stuff so fast even several layers of stainless steel (which you can't even get in vanilla!!). You could argue that it's because I'm on insane and should lower the difficulty, but it wasn't this bad in A16. They really dramatically upped zombie damage in A17 to obscene levels.And none of that really helps too much since the zombies all get a massive bonus to damage when they're in proximity to eachother, combined with their psychic pathing that makes them focus on the weakest block.
Unless that's changed with new updates, been awhile since I played a17.