This entire series is a giant deus ex machina. Yuusha seems to have every power that is required by the scenario or just cool for the moment, while Maou just pulls from thin air one convenient invention after another. And if that's not enough, Onna Mahoutsukai just shows up when she's needed (being lost the entire time and found apparently by accident) with exactly the required deus ex machinas (not that we learn anything about her i.e. why there are three of her).
While the point of the story is that world can by changed without brute power, I cannot understand what stopped Yuusha from ending the war single-handed (not to mention that he had a party) before before the series started. He certainly could from what we see.
And to add insult to the injury, there's no real conclusion to the story. The last episode opens up more story arcs than it closes.
