I'm not a hardcore CK2 player (I'm probably one of the more 'casual' CK players with 300 hours under their belts, although I know that's probably not the strictest definition of casual), and I've formed at least one custom empire, and cracked 8K prestige with a character on multiple occasions. Never my first generation or two (particularly if you start early on and need to get your inheritance laws lined up to keep the right titles in the right places), but if you're ruling a decent sized kingdom or two, and have a decent enough dynasty, it shouldn't be a problem. You might luck out with people dying before their time and the like, but I don't think I've played a game of CK2 playing 'large' (obviously, deliberately playing small won't have you cracking 8K, but if you're a count in Ireland you shouldn't be forming an empire anyways!) when I haven't got over 8K in at least one or two characters.
And I'm not fully on top of the UI, don't care for plots, don't pay tooo much attention to what's going on (enough, but I'm no pro player). I note even the OP was actually able to create an empire, they just needed to be patient. I don't see the issue here. That said, I am a filthy casual, so maybe it's just me being oblivious

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