A small sidenote about Heroes, those who may think that… They play hero, and then they shouldn’t die, but to defeat all. (I myself have Heroic characters aswell.)
Remember something: Heroic Death.
Varian DIED a Hero, which to this day, most of us, if not all, love him and agree that he was a Hero.
To be honest your hero character can actually die a cool death, and that causing big impact with their death… You know, even they may be remembered as a Hero and others may afterwards fight in your name and memory, vowed to be avenged some day… Isn’t it cool? 
Just like how we vowed to Avenge Zul’jin…!!
That kind of death alone makes it very cool… And ORCS understand it WELL… TO DIE WITH HONOR, AND BE REMEMBERED AS A HERO!
FOR DOOMHAMMER!!!
For GROM HELLSCREAM!! (MU one totally.)
You can see how Grom died. 
A hero’s death.
Nothing wrong with being a Hero. But a Hero can have a really glorious death aswell!
…and one may not END with Death… Their Legacy may live on…!
…THE HALLS OF VALOR AWAITS…???
Tl;dr, a hero can have a cool, heroic death.
Also remember, power depends on the INDIVIDUAL, it isn’t like…:
“Oh okay you’re a warrior I’m a dk then i win because I’m a dk.”
A Warrior can be stronger than a Death Knight, depends on their power.
Something once Mion said, a Legendary quote which I will remember and apply to everything.
“Your character is a character before anything.”
She said about DKs, but anything really…
Power is subjective I’d say, really… Saying that a Monk WILL be defeated by a Demon Hunter depends on the partaking duo, not their class. And that isn’t -lore- , but part of character.
Of course some weaknesses and attributes can be lore, for example Paladins not being the fastest of soldiers, or rogues not bearing the most protective armor usually.
Villains and heroes can differ in their power, and anyone can lose really, in the end though? Of course… ALL BOW… TO DEATH…
But the struggles between a Hero and a Nemesis are what that makes it interesting, not some cartoon hero which just punches the villain, it dies and the hero flexes. The Hero being hero for the sake of heroism, and the villain for the sake of being evil.
Sorry it became a long text! And Sorry if i accidentally mentioned somethings wrong , possible with my current situation. 
Have fun!