Before I go on, know that whenever I say Cyber Kukan, I refer to the Cyberspace in MMZ3, and when I say Cyberspace, I mean the one in MMX4.
I went with only an Earth-Sun sized dimension for the calc mainly because I found it most easy to explicitly prove and justify with what we're shown in Cyber Kukan in-game. Remember that at no point in time we explicitly see a starry sky within Cyber Kukan which is why I refrained with going any higher (though tbf one can say it's game mechanics because that's what we're told by Hirondelle in the same convo that describes Cyber Kukan for us and your points regarding Area X-2, where Copy X's stage is).
That said, I believe that it is possibly much bigger than an Earth-Sun sized dimension, given Omega should be superior to other Mavericks such as Cyber Peacock who was stated to destroy the Maverick Hunter's Network System's Cyberspace (yes, there are multiple Cyberspaces in the Robot Timeline). Granted the means of how he'd do it are unknown, and there is no timeframe of how long it'd take him so good luck trying to use that bit for support, let alone a solid rating.
That and if we're to use the Remastered Tracks Rockman Zero Telos' (MMZ4 song remake album) booklet, it describes the Teleporter Circuit as something that resembles the Cyberworld from the Battle Network series. This is interesting given in lore of MMZ4, one of the navigators says that the Teleporter Circuit looks like Cyber Kukan. Though I feel like it's just the artstyle of the Teleporter Circuit stage and not necessarily the span and magnitude of the Cyber Kukan. But I could be wrong.
Like, I agree it could be much higher. I've been thinking about this feat and such for a good while now (since October of last year), and I believe it could be higher than just Solar System level. But I don't think there's any explicit showing or concrete information that concretely puts them at a higher specific rating like Multi-Solar System level.
Unless you all have anything to add or comment, I feel like Omega's rating, and as a result, those that scale to him, should be Solar System level, possibly much higher with a little descriptor saying the reasons. This rating... for the moment until there is, uh, more information.