@Marindor , thanks for the clarification
now I would like to shed some light on an ambiguity regarding cluture/mana buildings :
-when/if the culture/mana buildings we unlock during chapter research are not satisfying or tricky to use, event culture/mana buildings get interesting; a typical case is the arcane library, that gives very little culture with a reasonable amount of mana, and you need tons of them to cater for your culture needs;
-when/if culture/mana buildings in the chapter are good, powerful and balanced, like the weeping willow or the grape farm, then we can organise both our culture and our mana production easier and event culture/mana buildings become less interesting, they are only a plus; on the other end, getting pure culture buildings as an extra is nice under such circumstances
so it is not that we want all pure culture or all culture/mana, different people have different needs, but nobody needs a building that we can't know for sure what it will do next day
I have decided to go with a mix of high level pure culture (event buildings), powerful mana/culture (now having several grape farms) and some culture/pop
when the flourishing nut cave came and I won 1, I immediately used it to get rid of a pair of smaller culture event buildings that I had built as fillers sometime ago, because it gave much more culture than those combined for the same footprint, and I was happy with this new building;
now you change it overnight and I am stuck with less culture than before and I am forced to move it to a place where I could wish to use the space more efficiently, that is next to a street;
hence the frustration ...