---------------------------- Going for the Kill versus Omegon
A lot of people don't realize that Terrans made up many of the veterans for the original legions and the vast majority were never swayed by Horus or his dark cohorts to turn against the Emperor. Sure there are some such as Astelan of the Dark Angels that are a mar against everything right in the world but fortunately they are an exception.
To me that says a lot and it's something to be remembered. Imperial Fists' home world is Terra so in a big way they are all veterans. People like Graham McNeil who is no longer an author for the Black Library liberally took a dump on Imperial Fists to promote his favorite renegade legion the Iron Warriors. In truth if you ever would take the time to explore the official records you'll find that the Imperial Fists won the majority of their fights versus the Iron Warriors. It's also important to note that Pertarabo the Primarch of the Iron Warriors always chose not to engage Rogal Dorn in a challenge.
The Imperial Fists are an epitome example of a loyalist legion by simple virtue alone. As noted above Imperial Fists are often depicted as bumbling buffoons but nothing could be farther from the truth. It was Rogal Dorn that slaved the Emperor to the Golden Throne so enraged by the actions of his father during the final battle on Horus' battle barge.
If you follow the stories from the Black Library in regards to the Heresy the villians win every major battle right until the very end which doesn't sit right with me. This is one of the major thematic problems with how the grand story unfolds as a whole. Just think about it... Who ever won an epic fight with one blow delivered right at the very end? It doesn't work like that in real life so why should we buy into something so fantastic ?