Another thing, IMHE, the momentary flux of feelings described (If my understanding of it is accurate) is an experience of impermanence, but not yet a vipassana insight, as it has not revealed yet the true nature of the knowing mind. With direct experience of rise and fall of the knowing mind together with the object (the only point where paramatha starts to manifest), understanding of reality has a radical swicht, and the impact on meditator's mind is much stronger and it goes on increasing if practice continues.
That means, either samatha or vipassana as method CAN lead or can NOT lead to vipassana as result. When we use vipassana as method, our object is supposed to be paramatha but in reality, unless one has very sharp facuties, at first the mind can only be aware of pannatti. May be the actual difference between the two methods is in the intention of focusing: one is one object only, and the other multiple objects. And it is very probable that a meditator intends to do samatha but because of inclinations, the mind stays aware of many objects, and another meditator, intending to do vipassana, but because of inclinations, the mind is slipping into absorption.