Supposedly the fang of Haynek-whatever is just the fang of a lightning dragon set into the hilt of a dagger. And he was definately mortal seeing as how he died. Now, yes, dragons are supposed to be very magical, very powerful, very dangerous creatures; but don't go dismissing mortals offhand in their abilities. After all, they created an ascension machine that tripled as a mecha and a stabilizing point for creation. They're pretty handy.
For a weapon like Umbra though, it's a lot different.
In game statisics, Umbra has it's failing points, but in the Lore. Umbra steals soul energy, the strongest point of mortal magicka.
The Dragon...I have my own ideas about them and I won't clog this forum with them but I think the Dragon's were far more then mortal. I mean, god's can die. Well, correction, The Nine Divines can die, Daedra just go down the cosmic drain and ae recycled but still.
The Ascension machine was created by a directly...Immortal race, or was rather, made with tools from a Immortal race. The Dwenmer and the Chimer were a lot more powerful during those eras then their relatives are today.