When playing healer in high rank games, try to hide behind cover immediately when Atlas ults, as smart players will banish the enemy healer, sometimes twice for 8s without healing your team!
Atlas is high damage tank very dangerous on solo fight. He can undo all dmg he has dealt for quite a while. He also can cancel all healing (self and from others) you've gained. To counter him you should always be with an ally to put pressure on him.