Rowan knew his Twilight Bridge would handle any sort of undead that entered its bounds, so he was not worried about Third using it against him, on creating the bridge he knew that it should have the power to deal with the undead or Third would be able to grind him to death.
More than anything he was focused on the changes that had happened inside him after he had changed the direction of his evolution and recreated his Ouroboros Bloodline without the influence of Chaos Blood.
At this time his Ouroboros Bloodline was undoubtedly the strongest among his three bloodlines and although he had expected something amazing, it took a while before he reconciled what he was seeing with reality.
Rowan knew that he had become powerful, but he did not expect that he would grow so much, and he was glad that took the time to develop his abilities in the direction he wanted them to grow. Sheol who was once a Nascent Primordial Bloodline and his strongest had been dethroned.