Honestly, it feels like pretty much every book has Iron Hands in them. They were the most numerous loyallist Legion involved post-drop site, admittedly, but any book involved the Shattered Legions has Iron Hands involved, who near enough single handedly manage to fuck things up, and simulataneously be the most uninteresting characters written.
I'm not going to lie, I might be slightly biased in that I was never interested in Iron Hands prior to the Heresy information - they were just a legion which preferred bionics to tap into that Terminator-style vibe (with a part-metal, part-plastic tactical squad being produced for them around the time of when Matrix 2 and 3 were at their biggest hype, IIRC back in late 3rd/early 4th edition, IIRC), similar to how Tau tapped into Gundam interest etc.
Damnation of Pythos
All of these have major focus on the Iron Hands following the legions - Angel Exterminatus was notable for the Iron Warriors first major appearance, and how Fulgrim interacted with that, while Damnation of Pythos was meant to be "the return" of the Iron Hands to the screen. In addition to that, there are a ton of other references and inclusions of Iron Hands dotted about, where, they didn't need to be.
My point isn't that the Iron Hands are merely mentioned
in a novel, but that we get to see and experience the loss that come with a primarch being killed. That just hasn't been presented in any of the post-Fulgrim
novels save Pythos
The Hands were the secondary focus of the Exterminatus
novel, but that was almost wholly an Iron Warriors story. There was almost no mention of Ferrus Manus or what his loss meant to the legion. They were essentially just a kill-squad. Whereas Pythos
went into much more detail and focused more fully on the fallout of Manus' death. In particular the passages about the resultant intra-legion power structure, lack direction/vision, and competing agendas within the survivor group(s).
Feat of Iron
, the story from The Primarchs
had no relevance to the post-Isstvan Iron Hands. It was a snapshot from a battle that showcased zero creativity, strategy, or problem-solving ability from the Hands. And this was with Ferrus leading the attack. The message from this one was simply that the hands had gone too far in distancing themselves from the 'weakness' of the flesh. There was no disruption of power dynamics, as Ferrus appointed the leader of the fighting effort while he took his journey. So while they may have been mentioned, or even featured in this case, very little (or nothing) is made of what will happen to the legion once their primarch is gone.
Now it's entirely possible that I'm just dismissing these other stories because they didn't fit into the bos of what I wanted to read. That's a completely fair critique. But the description of the hurt, the chaos (pun not intended), and the general pall over the legion were what made Pythos
a huge step up from the other references to the post-Isstvan X Legion.