I often say, in other games too the game shouldnt be balanced around the "normal" difficulty, generally. Thus it shouldnt be gigaagressive, in this case. On normal. I think the hardest difficulty is which should be reserved for the bit "broken/op" mechanics. And between the two, the mid-hard difficulty is where the game should be the one balanced around. For the not-first-playthrough, when you are familiar with the game...
But ofc thats just my humble opionon, thats how it feels right to me.
Okay, now its not strictly related, but I have to mention that too: So HRE... So to first thing that comes to my mind about HRE, the first thing that like catches my eye is that the Emperor isnt protecting the HRE from external threats, like England, but mostly France obviously. But rather its like a race between Bohemia and France who "eats" HRE first. The one that's supposed to be protecting them is their biggest enemy. Which I suppose is less than ideal...
Okay, one more sidenote. Obviously tuning the AI behavior is one thing. Like you can say the AI France just wont attack HRE, cuz its coded. But the problem with that is, well first its not very realistic in general, not the most elegant solution, and secondly, the game has an MP mode too. So instead of tuning AI behavior instead mechanics should be added which guides the whole gamplay in a certain direction... Now one of those already is the Imperial Authority.
But as we can see, as it turns out, its not enough... So it should be tuned up and more mechanics added to it or sth.
Ofc there are many things I havent addressed now, but just a few things that stood out to me and wanted to mention.