My experience in Brazil: Uber is way cheaper here. Compared to what I paid in San Francisco, I'd estimate a ~10x difference. And things here are rarely 10x cheaper. The difference in restaurants is probably less than ~2x.
My point being it probably feels like less of a luxury for us than for people in the US.
I'd say it's probably the most popular app too. I've never met people who used others.
99 is quite popular in Brazil, and is often cheaper, but Uber does seem ubiquitous there and is the leader.