Its the -4 defensive penalty spearmen get against sword armed units that does it, plus the formation. But even hoplites to me should last a little bit longer than they do against romans. Anyways, I can only use thureophoroi to flank phalanxes with their javelins. If I charge before they're about to break, they get slaughtered when the rear soldiers switch to swords. Peltasts seem a better option.