I found this same topic concerning Silver Surfer vs Cythonna.
My complete response can be read there.
But for now, I don't think it makes a difference. Line up any of DC's or Marvels strongest characters, and I don't think many of them would even present a challenge to Cythonna since (1) she's a Goddess to a race of Kryptonians already millions of times stronger than humans; which means she's God knows how much stronger and more powerful than them. And (2) even Superman admits that "she possesses a strength beyond anything I've ever encountered". This is amazing because this means she's stronger than some of the DC villains whose strength completely trumps that of the man of steel's.
From what I've seen in both DC and Marvel, and based on the feats demonstrated, I don't care which line of comics they are from, or who, I doubt that few could challenge the Super charged, seemingly ultra powerful Kryptonian Super Goddess, be they Surfer, Thor, Hulk, or the many powerful super villains that trump Superman's strength. Of course there's nothing to prove any of our views, but I just don't think too many from DC or Marvel have ever been presented as so incredibly powerful as Cythonna, at least when it comes to strength.
Even if one of these could overpower superman, he'd at least give them a fight and it would be hard for any of these characters to do so. Yet superman didn't even compare to the vast strength of the Kryptonian Goddess who not even Rao could physically overpower. That says something. I just wish the creators had some kind of graphs available that would organize such information. But then again, it leaves more room for the fans to speculate through their own imaginations.
Either way I believe this is why she's not around and was written off after only one story that featured her. Based on the way she was presented, what even superman says about her strength after his first encounter with her, when only a backhand was enough to almost put him out, and the way she easily overpowered and "handled" superman (lol pun totally intended), I'd say she's too strong and powerful a character and would probably cut through all other heroes and villains in the DC Universe.
At the level of strength and power in which she was presented, and having more of it than anyone superman has ever encountered, it was either write her off in a good one time story, that would leave superman in a desperate one sided fight for his life and the fate of the world, or leave her in DC Comics as the incredibly powerful Super Villain who probably wouldn't have any trouble defeating all heroes and villains and taking over the DC Universe. But this wouldn't make sense because she should be able to just go in and kick the crap out of anyone, villains and heroes alike who dared to stand in her way, taking everything over as she wanted to in the first place. So it seems the answer was, "let's create one of the most powerful villains and characters we've ever created, but we'll have to quickly write her off because she's gonna be too strong to maintain her presence in the DC Universe".
Of course this is a major bummer, because after discovering this powerful Super Goddess as the awesome character she was for that one minute, I wish we could have seen her take out some of superman's greatest and most powerful foes or at least do to them what she did to supes. I think Cythonna was a fresh and exciting villain, and it would have been cool to see such a powerful female character whose physical size is just smaller than supes, beating down on some of the big boys like Doomsday, Darkseid, Apocalypse, Mongul, and tossing them around just as she did the man of steel.
Just my wishful thinking I guess. lol, but since I'm at it now..
BRING CYTHONNA BACK!! Have her beat the crap out of some of the other powerful characters, yes especially some of superman's greatest foes. She was so cool, original, and DC has yet to see someone like her or matching her strength since she left.
