It all depends on what is actually trying to be communicated. With your definition most meals would be plant based so why even bother to say it. With definition where plant based means no animal products it communicates that it is fine for vegans and it’s likely less offensive for people allergic to word “vegan”.
(Established) scientists have a long history of ignoring new theories not science itself. But that’s because at the end of the day scientists are still human.
Science is not great at working on a very short time scales. But give it enough time so more evidence is gathered and possibly some stubborn influential people (that can’t accept a new theory) die and generally we get closer and closer to truth.