If there is a scrappy fight which takes too long, I feel the team with Ana will lose because eventually she'll run out of heal-boolets and need to suffer that super nice reloading animation which takes an age and a half.

Meanwhile, the other team has a Mercy which start the game with a free-rez, can fly away from danger, has self regen and is halfway thru her ultimate already.

But it's cool because assuming Ana never misses a single shot, she has a slighty higher heal per second... while her ammo last.... assuming she isn't dead...