One of the reasons I don't like playing as balkan countries in ck2 more recently is that they don't have one of those de jure empires that they've added in that region at all, so I feel like I'd have to take control of byzantium eventually anyways, and if I was going to do that I'd rather play as a greek or georgian family.
Funnily both Serbia and Bulgaria were among the few states who actually created imperial title during the middle ages, but in game neither has earned historical or fantasy empire.
But who forces you to play as emperor? Being king is good enough for me and I rarely aim to create unhistorical empires or to usurp historical ones. I might do that, if I meet the requirements, but only if it amuses me and if I have good reason to do so. Naturally there's some sort of temptation to take at least Greece (including Constantinople) from Byzantium, but I have allowed them to live in Anatolia.