The phrase "are in the same league" suggests that two or more items, individuals or teams are comparable or equivalent in some aspects. However, the antonyms for this phrase could be "are not comparable," "are unfitting," or "don't measure up." When there is a considerable disparity between two entities, we could use phrases such as "not in the same category," "are not alike," or "incomparable." In contrast, if we are looking for a more straightforward antonym to "are in the same league," we could say that they are "out of someone's league" or "not on par with one another." Overall, the opposite of the phrase depends on the context and degree of the difference between the subjects being compared.