I find on the NYC course the most that my ride experiences slows considerably. The course is small and there are so many riders. In Watopia/London/etc riders are more spread out and there are more routes that do not overlap so I never see an issue.
What would be cool if you could say Hide All Riders, Hide Riders riding in Groups,Hide Idle Riders, Maybe select riders from your region (NA, Europe, Asia, etc), select riders from your country, select riders with the same ability (Level range 25-30, 30-35 etc).
I would assume this would help those running on older devices