The phrase "were tantamount" implies that something is equivalent or very similar to something else. Therefore, the antonyms for this phrase would be words indicating dissimilarity, inequality, or difference. Some antonyms for "were tantamount" include antithetical, conflicting, contrasting, different, dissimilar, opposite, unequal, and unrelated. By using these antonyms in place of "were tantamount," it is clear that there is a stark contrast between the two things being compared, rather than them being nearly identical. This can convey a different meaning and tone in communication depending on the context, so it's important to choose the appropriate word accordingly.