It’s not like it happens with every hit, lol.
The regular attack also seems a bit overpowered. Especially considering that the banshee growth rate is +3.
Let me explain. 2+1, with an additional +1:
1) requires an extra building, 1 day, and resources for it. If it is built, it is significantly later than the basic dwelling (which, in the case of 3, would immediately have an increased growth rate), due to the acute shortage of mercury.
2) plays no role in the growth rates from external dwellings.
3) does not provide any unit production (i.e., does not provide an increase in the number of units per day of construction, unlike a simple basic dwelling with an increased growth rate).
What? What nonsense are you talking about, sir?