An important factor is knowing your audience. Writing a book review? Go ahead and use "bildungsroman". A scientific paper? Neodymium, amygdala, or ionosphere will probably be understood.

The goal of a writer shouldn't be to confuse their readers or make them feel dumb, but they also shouldn't sacrifice a perfectly fitting word that 90% of the audience understands for a weaker substitute that 100% understand.

I often look up words when reading. Sometimes new words, and sometimes words I have a rough understanding of but am curious about their dictionary definition. I almost never see as the author's failure or mine.

Many of the words in this list I've never seen before, but I don't think that means they should necessarily be discarded. And I wouldn't want writers to avoid words like bowdlerize, vestigial, avuncular, defenestrate, palimpsest or sinecure just because they could be replaced by a more common word or phrase that means almost the same thing.