Lex made himself insignificant. He made himself seem unimportant, barely able to do more than retain the protective barriers. On one hand, he did it so that the Defiler would treat him as relatively unimportant, focusing on Giselle himself and leaving Lex to his Profanites. This was so that Lex could study the Defiler a little more, and grasp the full scope of his abilities.
Even Sovereigns could not just outright change the laws of a realm, let alone an Earth Immortal, so Lex wanted to understand the scope and limitations of his abilities.
On the other hand, he did it so that he could genuinely finish the formation to disrupt the storm. Fighting the Defiler during the storm was an issue, but if the greater issue was that the storm itself was threatening countless lives. Currently, it was a greater threat to the population of this planet than the actual Defiler.
