Appear between the two armies, tell the nobles to get out or face annihilation and approach Angron only once he assured him he has no ill intentions, perhaps?
You're imposing knowledge you possess, as an outsider looking in, to the Emperor's actions.
Use the context made available by the fluff. The Emperor had no reason to assume Angron would go into a berserker killing rage. Every single Primarch he had met until then, even the sociopathic Night Haunter, had been well-balanced and lucid enough to allow for (at the very least) something resembling civil interactions.
By contrast, there's no indication that the Emperor had any knowledge of the political happenings on Angron's planet. More on this below.
As far as I know, it is said that the nobles cut them down. If this was just a cover story and the Custodes killed them all then its not helping either. Appearing in the midst of an army ready to fight to the death isn't clever, and if you die because of it you're getting what you deserve.
The nobles didn't cut Angron's followers down while the Emperor and the surviving Custodes were there. Nor is there any indication or evidence that the Emperor and the surviving Custodes killed Angron's followers. Even if they did, though, Angron neither knew nor claimed that the Emperor or his men killed them directly.
At any rate, with your final statement you are again imposing a context only a reader is privileged with. Nothing about Imperial starships sensors indicates they get returns like "there appears to be an army ready to fight to death on the coordinates you indicated your son may be." And, again, no in-story context existed wherein the Emperor should have been worried about a blood-bath. More below on this.
He didn't know Big E was his dad when he appeared. He didn't know he was there to make him a general of a legion of his own sons. He just appeared out of nowhere far too close. You'd expect Big E to be more clever than that. And as far as I know, Big E didn't really care about Angron, he just saw him as one of his gene-kids who were created to be his tools to conquer the galaxy. He didn't really try to befriend Angron (nor most of the Primarchs, though).
Angron's reaction would have been the same if any individual had popped there. Expect the Emperor to be more clever how? What previous encounter with a Primarch should have led him to assume that one of his sons--crafted to be brilliant geniuses, most of whom had an innate understanding
of who he was when he revealed his true self--would be swinging first and asking questions later?
How do you befriend Angron? It's specifically qualified that he was permanently damaged by his surgery, consigned to a life of rage and fits that interrupted his thinking process. Not even Horus, whose charisma was legendary, and who courted him to join him in the Heresy was able to reach him on a meaningful level. The only people Angron loved and cared about were the people he identified with on an absolutely fundamental basis: his fellow gladiators, who suffered and were damaged like he was; and, eventually, his own Astartes, who, tellingly, ALSO underwent they same psycho-surgery as their master.
Its not "assumed" because there is no info that says otherwise.
Actually, when you say something is assumed, you do so precisely BECAUSE all evidence points to it, even if it's not spelled out for you.
Also, you ignoring the whole issue of leaving Angron's comrades in arms to die having an impact on his relationship with Big E leaves a huge hole in your argument.
No, I didn't; and no, it doesn't. I said it was a tragic situation because (A) it obviously affected Angron deeply, but (B) the Emperor had no way of knowing their meeting would turn to bloodshed and (C) more than likely, it's not as if Angron's men really gave him much of a chance to stick around or a reason to come back.
... since [the Emperor] had all the resources to gain the knowledge he didn't have (which is apparently the only defending argument), yet he was in a rush to conquer a galaxy that could have survived the extra 10 minutes it would have took to bring himself up to speed on whats going on down there.
Genuine question: how?
I'm not trying to condemn Angron's warriors for possibly attacking--I already pointed out that they would have done so only due to their implants. Thus, that's no issue. The rest of your argument is said paragraph falls apart, though, when you consider that no other Primarch or Primarch's faction (go figure, none of them were implanted with chips that had them go from zero to KILL!!! in less than a second) felt the need to attack on sight.
If Khan is a clone than so are many of the Primarchs. Hell, the whole Horus Heresy is roughly Lucifer's Fall from the Bible.
I never claimed otherwise!
What I stated, consistently, was that every other Primarch nonetheless had more depth and development. And that is true. Name me one other Primarch that is so tied in to one culture. Guilliman comes close, but at least he summons TWO cultures and isn't named "Gaius Octavian". Corax even borrows lines from the poet whose works he lifted his name off of, but at least his Legion don't dress like 19th century Americans, and his range of activities goes beyond the poetry of Poe.
Even Vulkan, who has been as invisible as Khan, has more depth since:
1. He and his society are no a virtual photocopy of an existing culture, and
2. He's not named after the second most famous warlord from said existing culture.
My problem is that you're calling him a copypasta without him actually making an appearance, his Legion a ripoff without having a book or two to give the readers a better insight to their character, and that you're disregarding the few facts and implications that exist for no reason whatsoever. A fair approach would be "There isn't much written about him or his Legion, so I withold judgement, but what little there we know about them sounds promising". And thats what I'm missing.
First of all, the onus is on the AUTHOR to provide proper character depth and development. I am absolutely in no way required to like a character that has neither, besides direct dies to a historic culture and leader.
You are absolutely within your rights to like the fact that a fictional army is based on said things, and to look forward to the day when they do get books. But that in no way objectively prevents me from saying that I don't have to like a character that lacks any depth or development.
Again, it's the author's responsibility to do this. Period. They, for a variety of reasons, have chose NOT to do this in the 20+ years that this game has been about and the 15+ years that books, articles, and all sorts of other fluff were written about the various First Founding Chapters.
Furthermore, I absolutely stated that my view may very well change if and when the Khan and his White Scars receive the proper attention. For right now, though, I don't think it's either bizarre or unfair that I enjoy those Legions and Primarchs I can actually read something about more so than those that there's next to nothing on.
You do realise that this is a contradiction? You dismiss the deeds of a fictional character who is yet to get a book or short story written about him, yet you praise a set of fictional characters who have? Sounds exactly what I said: childish and unfair.
It's neither a contradiction, nor is it childish and/or unfair.