^this
CK2 is, with one exception I can think of, the same game no matter what DLC you have. The DLC just limits when you can play as, and who you can play as. The exception I can think of is the retinues DLC, and yeah that's pretty bad. But once you're in a position to have retinues the game is already much easier anyway so it kinda sorta evened out in an accidental way.
In a roundabout way, that describes this DLC almost exactly. Except that you could play the nations already, they just had crappy generic focus trees. Now they've got better ones, there's a slightly more fleshed out autonomy system and tech-sharing system, a few custom techs, but that's about it.
There was nothing stopping you going commie Canada or facist Australia before. Just now it's more fun, yet with bigger incentives to stay historical as well. There wasn't much reason to stay historical beforehand, now there's lots of reasons to go in any particular direction with those nations.
So maybe not CK2 levels of difference in ideologies/peoples/religions, but that's kinda baked into HOI 4 from the word go. Switching "cultures" is one of the fundamental reasons for playing the game, now there's "reasons". For the time period, the only two other cultures that could have any reasonable impact in game are neutral and not-involved, which would be boring. Getting 5 or so nations "culture identified" in a game with a fairly limited number of nations and cultures isn't too bad really for a WWII simulator. Commonwealth is a bit weird because they're spread out everywhere, but not such a bad starting point to see where DLCs are going, because they tended to have opportunities that say, Asian nations didn't have to go all whacky in WWII. Or different opportunities to fit into one of the 5 "culture" groups (Democracy, Commie, Facist, US aligned, own faction) in any case, and ones known about by a large percentage of the playing audience.
South America should be very interesting, and far more regionally based than this one.