Yeah, Alpine Snowboarding is unfortunately non-existent for the most part in the US. Though, there is a small, dedicated US team on the men’s side. I think Alpine Snowboarding is great for the sport though, since it adds diversity to the program. The biggest problem for the growth of the discipline is the specialized equipment required compared to the freestyle events (which generally just use generic step ups for the most part).
World Cup and World Championships are definitely the pinnacle of the sport for Snowboard Cross now, since the X Games dropped the discipline a few years back. (Which is a complete shame since (along with Ski Cross/Para Ski Cross) it was my favorite event growing up.)
The biggest events for Slopestyle remain invitationals generally independent of the FIS. For example: Laxx Open, X Games, Dew Tour, US Open. I still see many of the best competitors attending World Cup events though.
For Big Air, the World Cup has become the main focus of competition outside of the X Games, and even the Big Air competition at the X Games is very small, and somewhat of a side-show.
Halfpipe is more in line with Slopestyle. There remains a few major invitationals outside the World Cup/World Champships, but you still see many of the best boarders attending FIS events.
I wouldn’t call the X Games the “de facto” World Championships. They’re just to exclusive. Their focus on American competitors has stymied (or lowered the potential) growth of the sport in some ways. That’s just my opinion though.
I do agree that FIS events are only given the time of day for the most part because of Olympic qualification. I have suggested that it would be in the best interest of the sport to create it’s own federation. FIS contempt for Snowboarding is more evident when you look at the quota cuts by discipline for Beijing. Snowboarding has some of the great diversity in terms of competing nations and your interest, yet the FIS cut more quotas there than the likes of Nordic Combined or Ski Jumping.