So, what, I should write down all my previous experiences that just confirm this one interesting one I wrote about in the OP? If you have 50+ games under your belt in Europe, you know as well as I that what I write about is nothing new.
The HRE AI loves nothing more than to gobble up its neighbor.
In my view, it should be forbidden to HRE princes to fabricate claims on HRE land.
Mission, rivalry, diplomatic insult, trade conflict, enforce personal union, no CB wars would still be possible.
This would push the de-balkanization of HRE to its proper place - to the era of Religious wars (Deus Vult) and nationalism CB.
Those that want to expand within HRE would now be forced to go Protestant or Reformed, at the price of the possibility of simply being removed from the map. As was the case historically.
This would also mean that other European powers like France, Russia, GB, Ottomans or Sweden/Kalmar would need to work hard to support the heretic princes to bring instability to the HRE else they be facing a greyskin monster. The unification of Germany, HRE or otherwise, brought the biggest devastation Europe has ever seen.