Defeasible means able to be defeated or annulled. So, antonyms for more defeasible would mean less likely to be defeated. Some possible antonyms could be definitive, indisputable, conclusive, irrefutable, unmistakable, absolute, certain, conclusive, final, unquestionable, or irrevocable. These words describe situations or evidence that cannot be challenged or disproven. Conversely, "more defeasible" implies something that is prone to challenge or refutation. Therefore, antonyms for "more defeasible" would refer to things that are reliable, trustworthy, or convincing and cannot easily be rebutted or disproved.