Well first of all they don't hit you that hard you bounce of the ground and fly up in the air :3
Jokes aside, why not? Giants are equally strong!
The dragon's breath is really fatal! If you're a Dunmer then obviously Fire dragons won't do a lot of damage (same with Nords + Ice dragons) but it is really dangerous if you don't have resistance and if they bite you too.
It really depends because it's easy for me to kill dragons because I have a strategy where I hide behind things to not get hurt from their breath and shot at them with my bow, but it would be REALLY hard to kill them if you are in the middle of a Tundra, not being able to hide anywhere :/