I mean everyone there shouldn't be able to keep up with Omni-Man, Tao iirc is only MHS-rel and so is Goku at that point. Omni-Man is massively ftl. They are, even little things like dodging space debris or finding a planet would be impossible if you couldn't react at the speed you were moving, mind Mark tackling Allen into the moon shows that Viltrumites can react at rel-ftl speeds and there's also a guidebook that says Viltrumite senses scale to the speed there moving. Omni-Man literally oneshots the entire list with a single attack, Mash isn't even on the list but if he is, Omni-Man beats him up mid-diff. Vash iirc has a moon level attack but afaik he needs to charge up to use it and it wouldn't kill Omni-Man.