You know I seem to recall that historically Carthage got stomped by an opponent which quite specifically lacked a true warrior class, seeing as how the Romans were working off a citizen-militia system...
Another thing to note is that dedicated warrior classes can also be quite easy to subvert if you know what to offer - a combination of phat lewts and them getting to keep their old status and privileges has often done wonders to win an invader allies, and often enough they've been only too keen to take on mercenary service.