Tamasi wasn't always victorious in battle after battle; he narrowly escaped death numerous times, even more than Ash.
Though he truly was the pinnacle of humanity, able to resist the direct influence of Technique Spirit, he was ultimately just human. Moreover, a mage's various extraordinary techniques are unpredictable and unavoidable. Until mastering the Holy Domain, battles between mages are filled with uncertainty; a single unexpected Technique Spirit could change the course of a battle. And how much more challenging when it's between a mage and a human?
