What's extremely frustrating to me about monsters razing cities is that they still destroy the fertility of the city site, many months after the pre-release FE patch that supposedly removed this behavior. It is one of the most infuriating mechanics in the game. I stopped playing FE for months after a wandering abomination mowed through my armies and razed my capital city, and I've been extremely disappointed to see that nothing his changed.
I mean, as ridiculous as it is to have a city razed by wolves or bears, there are scarier things out there that can crush you even if you're fully prepared. Even without turning the world difficulty up, sometimes there's literally nothing you can do to save a city. A city can be attacked by freak creatures that are more powerful than your entire kingdom/empire put together. You can see some mega beast coming, but even stationing all your best troops in the city only gets them all killed.
I like that creatures powerful enough to wipe out a whole kingdom exist, and I don't mind if some dragon or elemental lord or titanic named creature that probably crawled out of a unique location actually razes the town after conquering it. I mean, unlike a cave bear or whatever, I can actually believe that this dragon turned an entire city into a ruin. What I do not like that they somehow destroy the land itself, making a rebuilding process impossible, even after you slay the monster or watch them move on.
Maybe if it did something interesting with the land, like turn it into a haunted ruin, or a huge lair for the creature, I wouldn't mind so much. But having the land reduced to unusable featureless flatland just feels broken and bad.