Diadorus, Nepos, and others speak of the reforms, but there is a larger issue, and that is of practicality. The Greek form of warfare was by no means stagnant, it kept evolving. Many of our 'hoplites' in the iphikratean style might have been called peltasts or other things by some ancient writers. Remember, the Romans misidentified most everything with a big oval shield as some kind of legionary copy, when the greeks actually borrowed from the celts to create the thureophoroi. Same concept.