It's true, the Gon race was strong. They had influence, and they had proven themselves on the universal stage. That did not change the fact that these Gon that Lex had met were slaves.
They were Heaven Immortals to boot, so the memory restrictions on them were too much for Lex to break through in a short while. Of course, if given enough time, he could do it - probably. But regardless of whether he could do it later or not, it didn't change the fact that in the middle of a battle, what Lex could do was limited.
He'd barely read any critical memories from Jeziah, though he wasn't too disappointed by that. Through his memories, he'd learned that Jeziah was a slave, but didn't know details of the slave owner.
For some reason, Lex had assumed that the owner was also from the Gon race - likely because in Jeziah's earlier memories he had been taken as a slave by one of his own race. That didn't change the fact that there was a possibility that there was something else going on.
