Well, dressage is a sport that, although I never did anything like these riders, I do at least have a more personal connection to, since I used to ride in my youth, like, at least in Germany, many girls from 5-15 do. It sure is a sport that requires some money, but at least here it's not really an "elite" sport, it goes deep into the middle class, and is probably, among girls, one of the most common sports, maybe even
the most common one.
Of course the equipment requires money and only a few countries really compete, which downgrades it a bit, but that can be said about a lot of sports, from most winter sports to track cycling. (How many velodromes are there in all of Europe? While Germany at least is full of indoor riding arenas, there is at least one close to every small town.)
Then there is the question of "how much do you really exercise and do you have to push your body to the limit?" I'd say that it's definitely some very decent exercise and you need to be pretty fit, although a "peak physical performance" like in running, swimming, cycling... is not required. At one point it's more about concentration, body feelings, body automatisms and reactions. You could argue that that is not enough, but then you should get rid of many other sports first.
Equestrian surely is very problematic because the horses aren't always treated like they should be. That's my major problem with it. Better controls and actions in that regard are needed.
Skateboarding sure is a sport, why should it not be?? Likewise surfing. Although surfing is not really a viewer's sport when there are no waves... and in skateboarding I would like an age limit, that you need to be at least 15 to take part in WCs or Olympics, similar to figure skating. I fear that young people are pushed too much towards risking more and more for the fame while they may not have the distance to see that sports, winning and glory may not be everything. Instagram already has this effect, the Olympics shouldn't. (Of course young gymnasts already do as well, the risk seems to be greater in regard to other body parts than the head and spine, though.) But at least skateboarding is something that people really do in their free time, a sport that does have a broad base, not one of those nobody apart from competitive athletes ever does.
Synchronized swimming... yes, I watch a bit of that. I used to think it was hilarious, the make-up does have that effect. But then I realized what a hard sport it is and also, somehow, this video made me fall in love with it.
View: https://www.youtube.com/watch?v=yhHzY_Au-9c