Great post ! I like when people like you provide detailed information and explain their opinion bringing facts and (specially in AoE) history.
I am not familiar with Chinese History, I’ve only read a bit after playing with Chinese here and trying to understand the Dinasty system. I was expecting it to be something divergent/ branching, in the sense that when you pick a Dinasty, you win some stuff (bonus, tech, buildings & units) and lose others, but instead they made it linear: just one Dinasty after another.
Would it make sense for you if you pick one Dinasty you get one of the trebuchets, and if you pick the other you get a different one? According to what I read, one of the Dinasties had a mongol as a ruler (or was heavily influenced by them) so it would make sense that it would be less defensive in that case.
This is the thread I wrote with my idea and I would like to know your opinion, since you know a lot about Chinese History:
I know that Dinasties followed one specific order, but I like this idea, hehe