Not only within the Buddhist context (but certainly in that context) there is a tension – sometimes a conflict – between what are called “gradualist” approaches and “subitist” (sudden) approaches.
But the opposite of “gradual” is not “sudden”, at least not in this context. It is, rather obviously, “non-gradual”.
Those who practice Mahamudra or Dzogchen don’t get sudden enlightenment with no work, no preparation, no effort, no good fortune. Generally they do similar foundation practices, purification practices, practices to increase merit at those who see themselves on a gradual path. But these things are done in a different light, as expressions of the underlying, inalienable presence of the enlightened mind, not as the pedestrian performance of a strict, sequential recipe.
The difference is quite subtle, and it’s easy to mistake the one for the other.