Well, that seems to be a given with Paradox games
At least in regards to Russia/Balkans.
Well, honestly, i didnt find Russia that bad at all. Sure some borders were kind of funny, but at least most provinces are placed at worse roughly where they are in real life, and most of the rest of weirdness in Russia comes from bad map projection (as in EU3).
One time i sat down with the intention of reworking Russia, and soon after i figured out that my Russia was not that much different than Paradox (map modding is kind of my thing, and Russia is my favorite place on earth <3). The only place id rework is Belarus.
Balkan on the other hand is simply ridiculous. As duhsveti said, this is, id say, the second Paradox game where Croatia wasnt done that bad (its mostly quite ok, no Zagreb in Istria, huge improvement), but Serbia is just omg. For Christ's sake half of it is Bulgarian XD
Oh and yeah, funny thing is, old Yugoslavia (Serbia+Croatia+etc) has much bigger population than Scotland (even Serbia alone does IIRC), yet Scotland has something like 3 X more provinces than ex Yu combined, and also some crazy number of settlements in comparison. Thats how unbalanced the map is.
edit: it obviously works for vanilla CK2, but i doubt you could fit all the individual tribes on it, at least the south Slavic ones.