the rules of competitive is to play to the best of your ability and knowledge to win a game
by not swapping to zarya (or mirroring orisa) when the enemy tank goes orisa (if you are aware that zarya/orisa/sometimes dva is the counter), you are not playing to the best of your ability.
Trust me OP, Zarya and Orisa are the last two tanks you wanna see me swap to, theyre the only tanks I cant play.