I wonder if it's possible to program that it's weaks instead of strong? If so, I'd love it. Right now, I'd love to be able to assist people in rebelling from HRE and have it matter, as it is, it just slightly redirects their attention to italy for a few years and then they're back to bullying everyone around. Hell, I've had italy become entirely german a few times, which removes them as revolters half the time. -_-;
In nearly all my games they end up completely German. At most, maybe a couple duchies/counties will remain independent. The only times they don't is if the Kaiser is quickly replaced/killed.
But I love the idea of it being weak claims instead of strong. The revolter gets their independence, players can't outright abuse it as easily, and there has to be a certain set of circumstances for the old liege to get their land back. The newly independent realms don't have to worry about being gobbled up unless they give an opportunity for a weak claim to be pressed (which means, ideally, they'd then only revolt if they feel they have a strong enough person on the throne to get away with it). Which is also a point: the AI would then need to be smarter about it. While Matilda of Tuscany may love to revolt against the HRE, she should also recognize that she'd then be one of the only realms easily re-absorbed into the HRE due to her having lady parts.
So yeah... those are the two changes that could go a long ways towards helping balance the HRE (and other large realms): changing claims from independence to weak, and making naval invasions a bit more difficult. The Reconquista started in Iberia and "continued" into Northwest Africa through Iberia for a reason, and that should be reflected in CKII. If the HRE pushes down into Trinacria, sure, then maybe they can make an argument for pressing into North Africa. Maybe make holy wars only possible against neighbors like Muslim invasions, or within a certain "distance" using a similar formula to the old revolt rules... though I guess that already exists to some extent, given that you don't see England declaring holy wars for Fez.
In addition, the latter one would also help make Crusades a little more "special", in they'd grant a non-Muslim neighboring realm the rare opportunity to snatch up overseas territory. Instead, right now as a player, if I wanted to I could start off a game with France by immediately stomping the crap out of the North Africans. And the North Africans should really spend their early game worrying about the Shia Caliphs, each other, and the Sicilians... not the French and Germans.