Please, read carefully my AAR. I didn't vassalize Hungary, I inherited it. If you consider this not historical, just think about Prussia inheriting Brandenburg or Carlos I inheriting Austria+Spain+America+ Nederland+lots of Italian minors. All these was possible by Royal Marriages. The game just simulates this.
Oops. Sorry about that. I did not realize my error until after posting.
Would I be correct in assuming that only 'major' powers can inherit? That might explain your rash of good luck. You were the only 'major' power. And I have no particular problem with inheritence of other countries though I have some reservations which I will go into later.
(BTW, I think it was Brandenburg inheriting Prussia, not the other way around. Brandenburg would eventually rename itself Prussia because that way the ruler could be the 'King of Prussia' instead of the 'Grand Elector of Brandenburg'.)
When Poland or Portugal or Austria are my vassal, I'm stronger and larger than them, after having eating a lot of countries.
Still, from what I read from the AARs, vassalization and political annexation can come too easy. There rarely appears to be a downside. It costs money of course but countries will submit without too much wimpering. And there does not appear to be any diplomatic penalties either from other countries who either (1) want to remain independent or (2) fear you are gaining too much power. Unfortunately, I do not have the game yet so maybe I am misunderstanding something.
Still, I think these countries would resist if at all possible. First, I would not be surprised if Poland and Austria allied to put up a united front and thus be at least as strong as Greater Thuringen. Second, sure, you may actually get their kings to agree to a vassalization but the nobles or the peasants or the church may not be so accomodating. At the very least, you would expect that sometimes leading political opponents would rise up and try to claim the throne after the king had 'betrayed' the country. This would make vassalization and political annexation (and for that matter, inheritance) a bit more difficult - if you want the country you have to defeat the rebels. Otherwise, you must give up the attempt and suffer a drop in relations. This could also lead to wars of succession (free CBs for every neighbor, great power and countries with royal marriages). Third, I would expect a greater chance of rebellion in these countries until several generations had passed. Just because they submitted back when doesn't mean they are happy about it now.
I suppose this may be impossible to implement at this late date but maybe EU2?
Thanks for the AAR. It was interesting to say the least. And thought provoking...
