Board Thread:Ben 10 Discussion/@comment-31574541-20170322170014/@comment-24922135-20170403120219

I don't think he was defeated by a black hole, mearly exhausted mentally to the point where the voices in his head could not keep up the fight against Ben's full control of Alien X

If no one can beat and hurt Alien X in the series except another Celestialsapien, then why did they say that Celestialsapiens are among the strongest species

That should be self explanatory

why did say that they are durable and didn't say that they are invulnerable?

Because they are not completely invulnerable. As you already said, other Celestialsapiens (among other things) can still beat them.