Years ago, we were limited to 18 (20 with blueprints) units of a kind per town, but since we can get more by exploring, some people are able to have literally 500 knights, so if they attack someone that doesn't explore a ton like them, their opponent have no chance, so shouldn't there be some limit ? I already hear people who gets hundreds units this way saying "but this require a lot of effort to get those", sure, but the fact is that for people that produce their units inside towns only, with AS MUCH effort as you want, you will still be limited to 20 per town. I also expect "with buildings, you can easily retrain units lost, while with units obtained from exploring, once they're dead they're dead": first, with an army of a thousand units obtained from exploring versus an army of 200 units all produced from towns, the explorer army will not suffer much loss at all, and then, those units can be obtained back by exploring more, as the only limit is the number of cells of a continent and it doesn't require exploring the whole continent (or even leaving his own alliance to explore cells already explored by allies) to already get hundred units.
Also with buildings you have a lot of population and bad culture, with exploring nothing at all.
When I see the incredibly good items an average mercenary require to be recruited, I really feel that something isn't balanced as berserker expected there. Oh and by the way berserker, yes, here is mainly how they get hundred knights: it's not even by meeting a lot of "survivors" POIs, it's by using Kungfu masters: making like 72 nomads from 4 horses world resource inside towns, sending them all to kungfu masters, having I think a quarter transformed into better horses, retraining 18 horses, sending the 90 horses to another kungfu master, retraining 18 horses, sending the 108 horses to another kungfu master etc.