Not a biggy, but it seems that the majority of havens fall the very first time they're attacked. With those that do survive generally falling the next time they're attacked (all of this dependent on the player not intervening, or failing to do so successfully, obviously).
This is fine in some cases of course, it'd just be nice to see a greater range of haven survivability. Some fall immediately, some survive only one or two attacks, still others manage to weather several assaults, some refuse to be killed at all, etc.
Or maybe it's just bad RNG on my end that 98% of havens are made of lollipop sticks and tissue lol.