May I ask what city you live in? I live in a fairly small one, and when I go to raids, it seems that people either stick to themselves or to the small group they go with. In addition, I think the raids aren't really set up well to be something fun to repeat. As I've said, I think the battle system is incredibly boring, has a laggy feeling to it, and is one of the strongest deterrents against wanting to do raids. Since you can only really do 1-2 raids per day without hoarding coins/spending money, and since the pool of Pokémon available in raids is fairly small, there's also not a lot of reason to keep doing them. There's also the limited time frame-you can only really do raids between 5 and 7 pm outside of the weekends. Finally, there's been lobby issues at most of the raids I've gone to, which is a bit shocking because that's been an issue for almost a year now. I fully plan on doing enough raids this month to catch a Latios, and I might do a few with my brother so he can catch one too, but I have absolutely zero desire to do any outside of that.
I agree that the system does work to an extent, and I'm happy it works for you. However, I think the system could still really use some major improvements. I think a lot of the reason that social apps are required have less to do with the raids being challenging, and more to do with the game just lacking features to successfully bring people together for them. I think that right now, there are so many raids that I just assume most of them aren't worth going to because they usually aren't. I can see why lowering the amount of raids might not be the best solution to this problem, but I still think it's a problem that could be solved (perhaps showing people how many people are at a raid before going to it would help). I think that the system does work for some people, but I don't think it's working for as many people as it should be.