R’ shechter’s holds this to no longer be true and that rov cows are treifa.
Unless you do x-rays on the cows (which there is no chiyuv to do), the halachah assumes rov are not treifos. The fact that rov cows are found to be treifos after shechitah is of no halachic import; extrapolation is statistically important, not halachically significant. (This is how I understand R’ Elyashiv’s reported response to R’ Schachter).
There is no pssible way for the metzius to change; rov is not a statistic (which is subject to change), it’a a “chok hateva”, as recorded in chaza”l, and can never change.