I am ballmain in masters and only swap very rarely, even if I have a lot of counters. Many teammates always tell me to swap. Personally, I want to learn to play with ball, no matter what the enemies counterpick, because I think individual skill is more important than always being flexible and counterpicking.
Better to master 2 or 3 heroes than try to flex all of the time.
As a Lucio main, I know I can perform WAY better on Lucio against his counters than I ever could on Ana or Bap, for example.