I've been playing my Roman campaign and it seems to me that some factions, particularly Diadochi, seem to have an extreme over-representation of Royal Guardsmen units in their armies. I've compiled screenshots that show every large concentration or stack of Egyptian Troops I've been able to find just scrolling around, and I've found that probably half of the Ptolemaic Army could be considered 'Royal' grade.
The last screenshot is the only example I could find of a 'reasonable' Egyptian army of any size. I also always think it's interesting when you see an odd unit, like Cretan Hoplites out fighting in Mesopotamia since Egypt hasn't owned Crete for over fifty years.
Keep in mind also that there are many Basilikoi Peltasti hanging out as garrisons of cities too. Ultimately I think this is because late-game, once a city is fully upgraded in barrackses there is a dual problem of a computer losing access to some lower-tier units (Like Thureophoroi) while also being able to recruit their higher tier units all over the place. I think it might be a good idea to limit the recruitment of some units to only certain cities - like Basilikoi Peltasti, Agema, and Agema Pikemen to Alexandria, Thebes, Antioch, Seleucia, and Pergamon for all of the Eastern 'Diadochi'. It seems to me that there should only be half a dozen units of Basilikoi Peltasti and Basilikoi Agema total, even in a large-Egypt game like this, and maybe a dozen Royal Pikemen in total.
Edit: This would extend to other factions as well, like Sacred Band only in Carthage and a few other select places, the same with Armenian Nakharars etc.