Apologies, it came across as implying that Slavic areas were inherently backwaters, as you referred to "totally assimilating to the German sphere". Especially considering it would probably be a relative backwater regardless, given its peripheral geographical position on the edge of the German world.
It should also probably be said that Slovenia was/is the richest former Yugoslav republic per capita, and in PPP per capita in 2015, Slovenia was just behind the Czech Republic, and ahead of the following Slavic countries:
Croatia, Serbia, Bosnia-Herzegovina, Macedonia, Montenegro, Bulgaria, Slovakia, Poland, Belarus, Russia, Ukraine. Basically all of them except the Czech Republic, and that leads Slovenia by not a great deal, whilst most of the poorer countries are left in the dust.
Sure, Slovenia is small, but it isn't really a backwater.