What was Etraeus' point with his three planet demonstrations?

The first seemed unrelated. Like "Hey, look, there's stuff in the sky". Random ice planet floats around and everyone takes frost damage attacks.The second actually has a point. A green fel-esque planet and demon-oriented fel flame attacks. He tells you of how he saw the Legion destroy entire worlds, and asks what chance they would have had to stand against them.But the third one tells a different story. He asks if the Legion wasn't enough, and shows you "the true horror of our existence", planets fully infested by Old God tendrils which reminded me of what Malfurion tells you Ilgy'noth was trying to do in EN.Was he basically saying that while the Legion was a threat to the world, the Old Gods are far more dangerous and that part of the motivation for the Nightborne teaming up with the Legion was to prepare for that eventual conflict?Or was he simply giving us a planetarium slideshow of neat celestial objects he found with his Arcanoscope?Maybe I should get back to coding...