The Zombies and Crimson Iron Ants that Zhang Yanhang encountered had single-digit Intelligence Attributes. Even the Lord Monster Tracker only had 10 points in Intelligence Attribute, which was far from Zhang Yanhang's—it wasn't even in the same league.
Zhang Yanhang felt that, in terms of strength, Supreme Will was roughly on par with the skills he acquired during his First Tier Period. Although it might fall somewhat short of the most powerful Technique Immunity, it was at least on the same level as Seeking Fortune and Avoiding Evil.
After all, you can't hang around the riverside without wetting your shoes. Although he hadn't yet encountered monsters proficient in that type of attack, Zhang Yanhang was certain to face them in the future. If he didn't have the protection of Supreme Will but still chose to charge in headlong without precautions, he might find himself embarrassingly capsized in a gutter.