I’m currently playing EU3 + Heirs to the throne. I’ve no problem loading the game quickly on my laptop, so I guess it isn’t a design issue.
For the rest, I can’t help because I never played without all three expansions, so I can’t compare (I had only played EU 1 before, a completely different beast)
That said, France doesn’t appear unstoppable to me. Until now, I only played 4 games, with Britanny (I got crushed in quick order by France, but that was to be expected), Hungary, Dai Viet and Austria. With the latter three countries, France wasn’t really a direct concern, but still I don’t think it was unstoppable because :
-I’ve seen the AI form Spain with roughly the historical borders, and keep her ground, and if the AI can do that, a human player most certainly can too. In another game I also saw Burgundy developping into a major power and holding its ground (that included good chunks of historical France) for quite a long time.
-Now that I’m playing a major power for the first time (Austria), I could destroy France any time I like (or any other country for that matter), so I tend to assume it would be the same with any other major power, including Castilla.
-Finally I didn’t notice that France had a huge tendancy to turn against Spain. It seems to me that she’s usually more agressive against England and Burgundy, for instance.
I don’t know for sure in what supplement the “lucky countries” feature was included. But France is one of the default “lucky” countries. If you had trouble against France, did you try to set the “lucky countries” to “random” or “none”?
Also, did you take your time? You’ve some 420 years to win, and it doesn’t really matter much if you’re on the defensive or even lose some provinces at the beginning of the game. In the long run, with an human brain you should outclass the AI (for instance with a better colonization, trade income, conquest of North Africa, whatever…).
Also, how were the alliances? I’ve noticed that the AI countries tend to stick with the allies they made early on. Playing as Hungary, I’ve been blocked by an indefectible alliance between Austria and Poland/Lithuania, for instance. Which means that the alliances formed at the very beginning of the game (the very first years, even) can have a huge impact. If you let France ally herself with England+Portugal, for instance, you’re going to have a problem.
That said, France is indeed on steroids. That would be because it’s just so filthy rich.