MiscMods fixed this. I agree it makes pretty much no sense. Units of the same tech level are somewhat different (notably the Ottos have some pretty sweet unique artillery that is brutal in a siege) but they are generally balanced. I've been playing it lately and sometimes if I have a close-tech province with a foreign core I'll build some of their artillery, since Eastern cavalry usually has better defensive shock and it makes for a good mix.The point of the lower tech speed for non-Westerners is that so they can't have the same level of tech that Europeans do, which is fine, but what Paradox has done is create a double penalty that gets quite severe the later in the game you get.