Read Necropolis
Gaunt finds a chaos spess mareen in a tank that is basically a giant pyramid of baneblades
It is very much an OH FUCK ME moment
Also in the first book just two chaos spess marines wreck some serious shit, and chaos space marines continue to do some hilarious fun shit (Dorfy Fun). The pinnacles have to be in the Saints and Traitor general bits, I can't remember exactly when, but one of them has a team of xenos assassins and chaos servants on a mission - one of these servants is a dreadnought that bursts through the ground and goes all REEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE. It is very destructive. Veeerry destructive. The traitor general one has the elite of the elite of Gaunt's Ghosts running around on a chaos planet, and before long they attract the attention of chaos space marines. Shit goes down.
Also in regards to cactusnought, it was already very damaged. It couldn't even see them, because the damage was so severe.
If that's the one set in Vervun Hive, I've read it. Was less than impressed.
The appearances of chaos marines in the Omnibus I read consisted of some World Eaters attacking a tank convoy of Hellhound variants, ripping tanks open with chainaxes and then getting casually massacred as the intro for the Ghosts into the story, Iron Warriors being present in a fortress that the Ghosts were able to literally walk into more or less by accident and who got shot by the aforementioned overcharged lasguns and died, and the champion in the pyramid tank who shot Gaunt and failed to kill him because of a wafer of metal and then died to a human stabbing him with a power sword.
EDIT: The funny thing about helmets is that most of the time in the chaos marine books they got blown off by point blank bolter fire anyway.
So when you say that 'Others did it better', you gotta keep in mind that 'Others' did it later, when GW had decided to turn up the grimdark dial a little harder.
The first 40k novel was apparently
Draco, originally published as
Inquisitor in 1990, now part of the Inquisition War trilogy. GGs was first published in 1999, so there were prior 40K books to set an example. Though Black Library itself wasn't created until '97 apparently, and the first novels were published by GW Books and Boxtree if Wikipedia's accurate. Since BL has them now I'd assume they were published under GWs license.