In mode of expression, you mean? Or are you saying that they literally say very different things? Is there a particular difference or differences that you’re thinking of, that you might share with us?
This super over-generalized question with a lot of assumptions originates from my reading of this Wiki article:
en.wikipedia.org/wiki/Novum_Testamentum_Graece
As you said NA is simply a compilation of manuscripts, so I think this part of the Wiki does not elaborate on the methodology well enough, or it simply is a distortion of the Alands’ scholarship in favour of one’s private agenda.
As you said it’s impossible to render a word-for-word ‘faithful translation’ while avoiding any ill-presentation on the cultural context. This I can say according to my daily reading of the Liturgy of the Office in Latin. The Lectio Altera in the LOTH is usually a writing by a prominent Church Father, each having a different prose style. While I’m not a Classicist, my limited Latin knowledge suffices to let me see the nuances in particular sentence structures, word order (and hence the emphasis), subordinate clauses, word choice, tone, etc., which are hardly translated in English. Let alone the fact that quite some Latin readings in the LOTH were directly translated from the Greek, giving a queer sense of ‘non-Latinity’ as compared to other Latin Fathers - and needless to say the education background and target audience influence how the prose is laid out.
I am curious about the exact manuscripts used by St. Jerome which are no longer extant. But I guess this question might not answer the question that manuscripts of the Vulgate (as inferred from a ‘reverse translation’ of the Vulgate?) show drastic discrepancies with NA Novum Testamentum Graece.
Well, after all, I have faith in the Sacred Tradition. But the Wiki table is indeed of academic interest, though my Protestant friends might not be really convinced with the Tradition.
N.B. My general observation is that Systemic Theology develops well within the Catholic Church while Biblical scholarship is relatively handicapped.