The statement was made prior to both of them, by someone who didn't work on either
and it was his opinion. And to add even more, in the video u send the writer even says Viego will gain power ups as time goes on, so he was not talking about Vex+Ruined Champs mega amped Viego when he said Morde would beat Viego.
Even if we take that as a literal one, rather than flowery language and hypeup, it does not by any measure mean celestial realm is one of those which would be the only relevant one. But again its hypeup that should not be stretched to extremes, same way Fiora being the greatest duelist of Valoran doesnt make her the strongest swordfighter ever, above Diana or Leona, but more so compared to those that would be well known around Valoran.
This statement comes from scathlocke
who notoriously said twitter comments are opinions.
This statement is talking about people like LeBlanc and even then it's not entirely true cause we know Rell is capable of stopping Mordekaiser at least once if he came back, this is just saying if he found a way to return he'll always comeback using that way even if he dies morbillion times.
No, Ashlesh
tried to consume realm of gods and he got beaten and sealed. The cards do not depict any form of struggling all we see is Mordekaiser's goon tied up, and in the other we do not see Nilah at all, it's just one of her crewmates.
This is clearly the account being sarcastic and posing as a Mordekaiser follower "Our Lord will crush it", to promote his LoR card. Also the same account posts stuff like these;
Apparently Elder Dragon makes convos burn in envy but he gets ridden like a dog by tryndamere, or this
Apparently Akshan, Sett, Twisted Fate and Jhin was chilling in Shurima at some point in time.
Apparently Elder Dragon and Asol arguing about who was the bigger dragon wiped out the Riot's irl images.
Not to mention the literal channel reposts fanart and similar stuff, these statements are irrelevant.
But even if we take it as litterall this would be only be talking about a post sentinels of light/sealed Viego, the same guy who lost his mist powers, was rejected by Isolde (his love for isolde is one of his power source) and got one tapped by Gwen with no counterplay.
Vex picked Viego cause she thought he could bring her death+she liked him, not because he was the strongest he literally was far from it BEFORE she amped him.
This is completely irrelevant Mordekaiser could train a billion times harder than Viego and be morbillion times more skilled, this would not prove he is more powerful than him. This is like saying Batman is stronger than Superman cause he trained to become super human while superman was born super.