For sure, "specified-fonts" is still required. It distinguishes an iBook that has actually been tested and verified to look acceptable on iBooks from a file that has not. The assumption is that old books are much, much more likely to be broken. Thus, in EPUB books that lack that addition, all font specifications are just plain ignored.
The workaround where you have to add a tag inside the paragraph tag, however, is no longer required. It is a crude way to add specificity so that iBooks knows that some special piece of content should not
change fonts along with the body text, but it is not a very good way.