Have you read the ultramarine series? That goes along with the iron warrior series?
Two ultramarines destroy honsou's fortress, wipe out most of what he was building and is pretty much stated that honsou loses a massive portion of his army.
Should I also go into detail about the banishing of angron, the loss of that warp device in the cain series or a host of other things?
I red those books and to be honest the IW did it mainly to themselves at least the warsmiths (re-introduced in angel exterminatus) did, I would not overestimate the contribution of Uriel and his posse.
Another example is the BL fight in the first ADB NL books, there also an example of how chaos inflicted a defeat upon themselves,
The banishing of Angron (you forget Magnus and the candle in the eye accident), I think you pass the point that there are still former primarchs active on the chaos side (Angron, Magnus and Mortarion (small reference in Pandorax), do not know about Alpharius and Omegon), taking the fight to the IOM, the last time a loyalist primarch did this was ...Dorn and he got blown to bits.
I can't recall how many GK got killed in the banishing, but a significant amount
@ COTE: I do not pressume to have the same knowledge over the entire 30k- 40k as you have, but absorbing punches would be the most appropriate description,