Which idea the Ferrus one? I actually dont mind it, at all. I do believe its premature, but thats because in my own head canon there is a difference between the Emperor of 30K, and the God-Emperor of 40K. In 30K, I prefer my Emperor to be a powerful psyker. In 40K, I prefer him to be near Warp God, and this has some canonical references with his potential death and rebirth as the Star Child, or simply being released from his bonds on the Throne to ascend.
To me, the kinds of things we see with LotD, and the Sisters, those are manifestations of Faith, which is really just another way of saying manifestations of Warp Power. In 40K, the concept that a God-Emperor could do these things makes total sense. They are just the Emperor pulling Daemon invasion (LotD) or granting boons (Faith) based on worship, exactly like a Warp God should (Chaos, Gork/Mork).
Now, I know that the early HH books introduced the concept of worship of the Emperor having actual results, just like we see with Faith in 40K via the Sisters, but to me and my own head canon, its premature thats all, in 40K though its fine.
As much as I fan boy for ADB, this was a section of MoM I didnt like, just because of where it is in the timeline. NP, I dont have to like it all.
As to the Anathema as Anti-Chaos in power, that idea has no basis in fact. The only 'anti-chaos' is Sister of Silence type soullessness. Flash forward to 40K, how does Logan harm Magnus? A Khorne powered Axe.
The Emperor's power, is Chaos power, or as we know it, Warp Power.
(on a side note, I like to think I'm mostly polite, if I insult someone feel free to call me out as its generally not my intent)