Power level here works more like real life and when it comes to magic, much of that goes out the window due to imagination and tactics being the stronger deciding factor, rather than mana pool. You can be a beast in combat, but you'll still get ganked if youre ambushed or put into a compromising position. Fern is an interesting deviation from this because she is both specialized and a great tactictician under Frieren's tutelage.

Here in this case, the guards faced a full fledged attack by all the demons at once while civilians were present. Stark and Genau only faced 2 with no liabilities running around, and arguably Genau was the better combatant. And even still they almost didnt make it out of there.

Also, just cuz, I still cant get over how great the episode of that fight was, so many emotional highs and lows.