why such a simple reasoning was not considered in the firts place. P-semiconductor and N-semiconductor were developed exactly based on the argument like yours. I think it'd have been pointed out in the very beginning if your argument is the THE one or the most important factor. There are many qualified chemists and solid state physicists with good chemistry training working in the field, not just those solid state physicists lacking proper chemistry training, you know.

The behavior of electrons in MO are not the same as in free atoms.Delocalization is important but notoriously hard to charactrize. I'm not sure how far your atomic orbital energy argument can go in MO, in ZnO in particular. You may consider writing an article to publish the result.