First of all, Mephistus was the one who brought up "Starry skies" as an argument. That's where the confusion came from. But the fact that, "those aren't stars" only makes the calculation even more arbitrary. If all we see is a blank background, then that just means absolutely nothing.
There are plenty of places in the universe with blank black backgrounds; you don't need to fly outside the Observable Universe to find one. The inside of a wormhole and there are plenty of those in the Milky Way Galaxy alone. But enough messing around.
Anyway, we cannot assume they just flew to the edge of the observable Universe in seconds based on a couple of vague statements and a couple of generic backgrounds with multiple time cuts in between. Also wasn't
Tails able to see the distortion from Earth? But either way, flying "Outside the Universe" or "Beyond this Dimension" ect does not equate to flying outside the Observable Universe. I never was the default, and it never will be the default. Also, we don't know what's actually outside the Observable Universe as it could just be more galaxies for all we know. And the Universe' space could be
Infinite for all was know.
The merging of two Universes has never had "The edge of the respective observable universes" as the assumed default. I've seen plenty of examples of having similar time cuts and blank backgrounds despite having starry skies in space normally and graphics capable of showing them. It still looks nothing but a bunch of baseless assumptions.
Also, Dargoo Faust and DontTalk have both made it clear that feats like this are unquantifiable for speed. And please don't use the Supporter/Neutral/Opponent fallacy. Saying that one has to be a die hard supporter to have the best sense of judgement is extremely arbitrary and don't need to explain why. And actually, AKM Sama said it's typically people who are Neutral who have the best sense of judgement regarding verses due to being more open-minded compared to supporters and opponents.
Also, I'm not the only one who disproves this feat. A lot of people offsite are talking to me saying this feat seems arbitrary. I will say, Matt already agrees with me as he has multiple times back when the blog still had comments but got removed due to creator changing their name. But as said before, it's only going through if other staff members and preferably ones knowledgable regarding multiversal and dimension feats look at it. DontTalk overall typically has the best sense of judgement. And as he said, 4-D space travel of unknown distance is the norm and not some high-balled 3D Space travel.