And what difference does it make?!!!!
Think about it. When I build these creatures (1-3 weeks), and when I recruit them... it's much more important which is the best creature of levels 1-3.
A lot is decided at the start. And later, there are already several castles, which often only need to be slightly upgraded. And not every game lasts until building a tier 7 unit. As for Fortress, I don't think the castle is chosen based on tier 7 creatures.