What do you mean by entirety? Assos Sefarim Harbeh Ein Keitz. In fact, we find areas where Bavli skipped something and we picked it up from the Yerushalmi (although Rishonim are indeed reluctant to do this, and they’ll rather look all over and dig for a Remez in Bavli).
Now, although if the Gemara left out a necessary definition on something menntioned in a Mishna, that would be telling, this doesn’t mean that every definition had to have spelled out.
Torah Shel Baal Peh has what to do even after we see the words of the Gemara. Our Sefarim shelves are pretty packed. Many decisions come from a posek’s take on a Gemara or Meforash, but more often than we realize, the reading is based on what was passed down. We can’t bypass our Rebbes just because we own a copy of the Talmud.
LF’s usage of Mesora is no different than saying ‘we don’t follow that’ or similar statements.