I don't know per say, that this is a bug, or a gameplay intent, but if it is, I think the arbalests HP and attack strength need to be lowered considerably, even if this is on hard.
When the attacks starts in this quest (I play hard and 30 waves), and the arbalests are the first attackers, you often get pulverized by them way to early, because they do WAY to much damage; already from the 1 or 2 attack wave. And they are also way to hard to kill from the get go 1 or 2nd wave. In my book, they should be at least 30 % weaker, so you don't get crushed to early on
When the attacks starts in this quest (I play hard and 30 waves), and the arbalests are the first attackers, you often get pulverized by them way to early, because they do WAY to much damage; already from the 1 or 2 attack wave. And they are also way to hard to kill from the get go 1 or 2nd wave. In my book, they should be at least 30 % weaker, so you don't get crushed to early on