For all intents and purposes the game has two types of cores:
First is the realistic core based on a nation's capacity to mobilise that state's population for its industry and military. More or less all cores in normal historical play are of this type.
Second is what I call the meme core, granted by meme focuses and meme decisions where all bets as to their logic are off. These only show up if something ahistorical is done like reforming the Roman Empire.
Only the first category should be given thought in any serious discussion of what should and should not be a core and for whom.
West Banat was desired by both Hungary and Romania. The Germans kept it under their administration a) as a carrot, b) to avoid favouritism, and c) to not worsen Hungarian-Romanian relations.
I agree. Especially with your definition for a core, a nation's capacity to mobilise that state's population for its industry and military. However, the problem is that the game still has meme cores on historical runs.
A lot of people complain that Hungary doesn't get a core on Banat. I find it unhistorical that Hungary can get cores on everything except Southern Slovakia. The other regions may have been previously part of Greater Hungary, but most of the population in the lost regions is non-Hungarian. I don't believe that a people who would see themselves effectively under Hungarian occupation would give Hungary an easy time mobilising that state's population for its industry and military.
In 1910, only 54.5% of Greater Hungary's population was Hungarian, excluding the autonomous region of Croatia within Greater Hungary. Out of 20.900.000 people, only 10.900.000 were ethnic Hungarians. Out of the 13.300.000 people that got separated from Hungary after the Treaty of Trianon, only 3.300.000 were Hungarians, and the only post-Trianon region outside of Hungary where the Hungarians would still constitute an ethnic majority was Southern Slovakia. I don't suppose there's any data for a hypothetical Greater Hungary in 1936, but it's safe to bet the population of Hungarians didn't increase in Yugoslavia, Romania and Czechoslovakia after 1920.
Hungary is not the only country with meme cores, some are no-brainers like Bulgaria getting cores on Western Thrace. Austria-Hungary on the other hand is part of the 2nd category where all bets as to their logic are off.