Comparison with Harry Potter isn't strictly correct, the wizards there have repelling spell, which I'm pretty sure can be cast to 100% repel bullets (this is assuming there isn't any special bullet-repelling spells developed in centuries since arquebus and friends made appearance).

Didn't Sasha put out 10,000 round per minute according to "Meet the Heavy"?
Its been so long since I played TF2. I can't recall how fast the heavy's gun could eat lead and spit death.