Zhou Tian initially decided to leave those three Ancient Powerful Beings behind simply because he suspected that they might possess certain Treasures he needed. However, that was all just speculation on Zhou Tian's part, and whether those opponents indeed had the Treasures Zhou Tian needed had never been confirmed.
Given the circumstances at the time, it wouldn't have been difficult for Zhou Tian to defeat those three Ancient Powerful Beings with his Ability. However, whether they actually had the Treasures he needed became an uncertain matter after their defeat.
Therefore, based on the situation back then, even though Zhou Tian had overcome those beings, the question of whether he would find what he needed was already uncertain.
