Factbook and Book Prioritization

The "Books From Your Library" returns mostly commentaries in alphabetical order and ignores my prioritization list. Is this the expected behavior?

As you note, the "Books" are mostly Bible Commentaries. For many other topics the Books would not be ones that can be prioritized, so I would expect alphabetical order.

You could submit a Feature request but it would require that the section be split into books that can be prioritized and those that cannot (e.g. books that are indexed only by page number).

What you must understand is that Factbook section that include multiple types of indexes none of which must be present cannot use prioritization because multiple prioritizations apply. The Commentary section includes only resources with a type:BibleCommentary and an index by Bible reference. Here the priority list you made for Bible reference can be applied. The same can be said of dictionaries where all books share a head word index so your headword priorities can be used. But in groups where some of the books only have a page number index, no priority list exists; or if a mixture of books some with head words and some with Bible references occurs, there are two priority lists with no logical way to merge them. What you appear to be wanting is that in all cases where there is an available prioritization lit, use it; otherwise use alphabetical sequence.