Lex disabled the spatial formation which allowed the two deities to reconnect to the space of the entire realm. As they felt their connections reestablish, the two held hands and began channeling their powers.
At this proximity, Lex had to bear the full brunt of their power, which was far from easy. The only reason he didn't have to use Harden, and other abilities to resist the pressure was because he was a projection. If his clothes were normal, they would have been shredded under the weight of the two birds oppressive aura, yet since he was merely a projection, his clothes rippled softly as if they really were being buffed by the aura.