Yes. It makes no sense to put the game with the historical representation of the world circa 1444.
If your proposal jibed with history, it might make sense. If Paradox's kludgy vassal mechanics accurately represented a vast array of historical situations, it might make sense.
When Constantinople was sacked after the Fourth Crusade, the splinter states had other names until one of them successfully reunited a notable portion of land (including Constantinople itself).
Names given by later historians aren't necessarily relevant. All the successor states asserted they were the legitimate heirs of the Empire and their respective leaders all claimed the purple. Whether they managed to get anyone to buy into it or even get a credible coronation did, indeed, depend on battlefield success.
Nothing about the start has changed. Nothing at all. They did not lose owned land or have their owned land altered in any way. In fact, the AI now actually gets slightly more prestige, due to having less uncontested core territory.
Simply not true. Cores make it easier to expand. Having lost those cores makes it more problematic for BYZ to expand into those areas. To assert that it has no impact on BYZ is just counter-factual. Ask any BYZ player if they would prefer to have the cores or if they don't care, if you have trouble believing this rather obvious statement.
What HAS changed is Byz popping back up for a visit decades AFTER being roflstomped by the Ottomans. This doesn't just happened sometimes, it happens most of the time according to others and in my experience and it is rather shocking when I play to NOT see a Byz re-emergency at some point if I'm not all over the area myself. This is the aspect that's being targeted - resurgent Byzantines well after being conquered - their actual start and the sack of Constantinople are NOT impacted by the removal of unowned cores or the denial of free cores in favor of claims should the empire re-establish itself.
I've only rarely seen situations such as the ones that plague your games. When I did, it's due to those nations being defeated or otherwise collapsing; situations where you'd expect revolts and splintering. This was a positive feature, not a flaw. But now, unlike most of the world, this area gets a pass on nationalist revolts, because ... reasons ...?
If it's simply the title of Emperor, or the color purple, that offends, putting GRE cores, or some other tag, would better address that. Removing the cores, however, makes those provinces less susceptible to revolts, which is simply a bad idea, particularly when they've been adding ahistorical cores and tags to other areas of the map. To me, it's less about this particular nerf to BYZ (though I despise the idea of country-specific nerfs where they is no compelling game-play or historical reason), and more about the fact that we're kludging together a lame response to a non-problem because someone perceives that these nations need help dealing with nationalist rebels? Or someone hates Purple? If there is a problem with the rebel mechanics, that needs to be addressed. If there is a weakness, specific to these nations, that should be addressed (or maybe they should be reversing some of the ill-conceived country-specific nerfs they applied to countries like the Ottomans in previous patches). But the current core nerf, while admittedly slight, is an overall negative for the game, with zero historical justification and precious little game-play justification.
If you want to nerf BYZ based on historical considerations, there's lots that can be done and you've got load better ways to do it, some of which have been suggested in this thread. Was that the goal? Or you can buff the Ottomans, if that's the goal? But kludgy, inconsistent tweaks to selected cores, based on nothing, is just lame. It's not an effective nerf. It's not an effective buff. It undermines the rebel system while covering up what may, indeed, be a weakness of it.
