He was the one who largely ensured Angron's defeat.
Source?
We have no idea how the rest of the fight panned out.
It could have been Captain Taremar that won most of that fight. Or the weapons of Enceldaus and Galeo that speared Angron's wrists. Or the 80+ other Grey Knights living at the moment.
Or, most likely of all, a more even contribution of everyone involved.
It is truly an immense feat, provided I could buy into such a thing. Which I'm not.
It's up to you to believe it or not, but I think it makes a fair amount of sense. Angron was being assaulted by 100 psychic powers
purposely created to fight daemons. Their very presence caused lesser daemons to vacate the matterium.
Hyperion, as I said before, had incredible amounts of psychic power. Combined with his Reflective Psychic...surrounded and connected to 100 of some of the most powerful psychic warriors the Imperium could muster...
I think it's reasonable. It was hardly Hyperion besting Angron in a one on one duel.
I'm personally of the opinion that if Angron
hadn't ascended, the Grey Knights would have lost. It was his daemonic nature that sealed his doom. A rock, paper, scissors sort of issue.
re are several sm pyskers who are among the most powerful ones in Imperium
You totally missed my apples to oranges analogy, didn't you?
And you're using
psychic feats as a ruler

? Wouldn't, you know, the breaker of the Black Blade rank higher than those feats?
If so, then by our own measuring system, then Hyperion would be a stronger psyker than those you listed.
And if the breaking of the Black Blade is NOT as impressive of feats as you listed, then Hyperion is in fact weaker than those Librarians...and his feat would surely be more believable for you?