I agree with you. I have units with heaver armor for Middle Ages, with some Canaanite looking stuff for Chariot and Horse Archers. I can see the Philistines adopting the Companion Cavalry, light ancient cavalry. Probably with the rider looking like Spearman1 of Toad's collection and armed with the same spear, only on horseback. I imagine a Pikeman being a cross between the Philistine Spearman and Sherdan. Philistine helmut, but with horns as well, convergence. Also with nice glossy silver armor, maybe with some gold. Longbowman could reuse that look, but with different armaments' of coarse. Then you would have light cavalry(medeval) and heavy(knight). medieval light cavalry would reuse the pikeman, the horse would have some basic, silver armor. The Knight would be the Philistine, but with a Dagon(the fish god they worshiped bronze helmut). The unit would have bronze colored armor, and a heavily decorated horse, with Dagon images or fish. Musketman would resemble the lighter spearman or swordsman in Toad's collection. Maybe bronze and gold clothing. Just because he already did it, Why not use the Arquibusier animations and such Toad.
Cuirassier, can either be a mounted gun user or a more advanced knight. I'd say both could be may. Heavier Knight Cuirassier I imagine like the Polish Hussar. Instead of Wings though, i imagine two fin like objects, bronze in coloration. Armor would look like the Knight's. Maybe some color changes.
Maceman would be a golden armored Sherdan type, with a one handed mace, and a shield with Dagon imagery. You could also have a Medieval swordsman, Peleset style helmut, gold armor, sword and same kind of shield.
Just some ideas. Up to Renaissance.
I finished a working Philistine civ. I will be posting leaderheads I've made but had yet to upload soon.