If the halachah is like the Rabbonon, what do Kohanim who happily drink wine today rely on?
The Maharam Shik (Shu”t, Yoreh Deah 214) writes: Ideally, we should follow the opinion of the Rabbonon who forbid drinking wine nowadays, however, it’s a gezeirah [decree] which the tzibbur [general public] can’t keep, therefore, כדאי הוא רבי לסמוך עליו בשעת הדחק – “under pressing circumstances, the opinion Rebbi is something that can be relied on”.
The Shach (Yoreh De’ah 242, Klalei Horah) already writes, that in pressing circumstances, when it comes to rabbinic enactments, we can rely on individual opinions. Therefore, in our case as well, not drinking wine is very difficult, therefore, we allow Kohanim to follow the opinion of Rebbi.