There were countless races in the universe, more than Lex could ever know. Of them, there were surely many who were monstrously powerful, perhaps even more so than dragons. The Celestial race was one such example.
If looked at only using face value, then dragons were born as Earth Immortals, but Celestials were born in the Celestial Immortal level. By that comparison, they were much more powerful, and indeed their influence was unquestionable. Lex knew this because the small bits of information the Rhinocentaurs provided often mentioned them and their Celestial court.
But while they were incredibly powerful, Lex knew no distinguishing features about them save that they looked very similar to humans. Similarly, the other powerful races he knew all had incredible powers, such as the devils unquestionable control over demons, but no race seemed to be as well known as the dragons.