Chaos worshipping nations: Exists
Thunder Warriors: "I'm sorry sir, you've thrown off the Emperor's groove"

Oh, right, the Heresy. The Horus Heresy. The Heresy performed by Horus...

That Heresy?

fails to mention the NON AGGRESSION PACT WITH THE ORCS AND ELDAR!!!!!
thats how strong humanity was in the golden age.

The saddest part, the thunder warriors loved the emperor so much, and were so loyal, that the handful who survived the culling held no grudge.

Eldar: Humans are xenophobic, brutal, and evil.
Humans: You destroyed existence.

The funny thing about the Apex of Humanity during the Dark Age was that their weapons were so utterly annihilating, that Orks DIDNT WANT TO FIGHT THEM. They would just get instantly wiped out. Always found that really funny.

Thunder Warriors: We did it, we won the unification wars
The Emperor: good, that's one less loose end.....

To give an example of how strong humans were in the golden age of technology: terminator space marine armor (which is the strongest and some of the most advanced the imperial has) used to be used for manual labor like logging and mining.

the primarchs get oinked by chaos
Malcador: Uh oh
Big E: don't tell me, we're about to go over the galaxy and subjugate all fallen human colonies?
Malcador: Yup...
Big E: Thousand years of battle in order to find my long lost sons?
Malcador: Most likely...
Big E: Bring. it. on.

The Emperor of Mankind: "Magnus, pull the lever."
Magnus pulls lever unleashing a bunch of daemons into the webway project.
Emps: "Wrong leveeeerrrrrr!"

As a Custodes player, I have no idea what you mean by E-Money being a bad Dad, He Treats us Custodes just fine.

And this is how the Emperor clapped the galaxy's cheeks

Whenever someone asks about the Unification Wars I just tell them, quote…“Imagine if Genghis Khan, Alexander the Great, and Napoleon combined, now imagine they went unopposed, and it all took place in Mad Max and you basically have the general idea.”

Didn't even bring up that the Emperor's real name is Jimmy Space, and that's why they're called Space Marines

46:04
Magnus: “I RIPPED OUT ONE OF HIS HEARTS, WHY DOES NO ONE REMEMBER THAT?!?”

Big E: I can't wait to make an alliance with the Eldar when I finish the unification wars!

Eldar summon Slaanesh.

Big E: Valdor, get the bonking sticks, THE HEAVY BONKING STICKS.

As a fellow newcomer to the warhammer universe I can relate to DK and feel like I'm getting more invested as its like I'm sharing in the same journey alongside him so this helps a lot. Keep doin what ur doin

Story of the Thunder Warriors:
"The keys to taking power are not the same as the keys to keep power"
- Some smarter than me man at some point in some time

You forgot to mention that the Emperor was a supremely powerful psyker, like the greatest psyker to ever live. Hence he was aware of Chaos and the Chaos Gods and the general state of the galaxy.