kinda... our best athletes tend to play other sports, and we don't have a very good professional domestic league. it's changing though.
Correct, the top athletes favour more profitable sports. There is a chance in the next 20-30 years that concussion and CTE testing will expand and decrease enrollment of youngsters into contact spots like US football and hockey. Theoretically, that would increase the player pool in US.
The bigger issue has and continues to be insufficient player development. Around the world (MLS is one of the exceptions) teams run youth programmes to help develop players. That is the primary source of player recruitment, finding a younger (even at age 10) and develop them over the next decade until they can potentially make the real team. In the US/Canada they use the same hands-off approach of the major sports.
Take for example Robert Lewandowski. He spent almost a decade as a youth player for various teams before he broke onto the "first team" of Znicz in the 3rd divisional tier.
The MLS is the top retirement league for aging stars.
Also MLS tends to get better attendance than top division in Brasil.
Average Brasil attendance for 2016 was 15,736.
Average MLS attendance for 2016 was 21,649.
The increased profile and money in the MLS has been slowly increasing the talent of US players, however, that takes time.
From my limited time in the US, the sport is considered a "hispanic" sport.