No, I don't think that would be correct. At least up to a certain point in time when songs started releasing as real singles with streaming services. Before then singles had at least a B-side and, thus, I believe the general practice was to tag the album as "Song title (Single)" which, by the way, is very similar to what you were suggesting in this post here.
Furthermore, we could discuss tagging "philosophy" endlessly, I suppose (I even like those kind of discussions, tbh) but my idea is more based around convienience and what people are used to when coming from other systems/players.
What would be the negative point in having Album Artist default to Artist if the Album Artist tag is empty?
Because the positives are prettly clear, I suppose.