The fact that you must be dragon born to kill dragons says alot.
In tamriel, yes Alduin definitely, mainly because he cannot be killed by anyone but a dragon born.
If you kill him, he is still alive, and can come back alive again, and again, and again. You have to absorb the soul of the dragon for them to be dead permanently.
Dragonborn mabye mortal but he is still the only one with the power to stop dragons.
I honestly found it difficult to see the dragons as any kind of legitimate threat. They're disorganized, unloyal, incredibly weak once grounded, do not make use of their "legendary" shouting powers, and their leader was an incompetent fool who missed at least three opportunities to put down the only thing that could allegedly stand in his way.
As it Implies their primary combat tactic is meant to consist of throwing themselves at the enemy repeatedly in the hopes of whittling them down due to being renewable unless slain by a dragonborn, I am not impressed.