It's not just Ex-Roulette. Whenever tank is needed in Trial Roulette, I get Garuda 80% of the time (6 times in a row now). Joined as healer when it was needed, got Ifrit/Shiva/Ramuh.
Maybe it depends on your class/role?

I can see AK HM being hard with 2 SMN and healer/tank not helping with adds...