Not even that meaningful in hindsight.
You can tell the same story of the defeat of Arthas the Lich King by saying Fordring went there and killed him. You can change some minor details, even mention that he went there "with his personal guard" if you wish, but not much changes. The same goes for Deathwing: Thrall used the full power of the Dragon Soul over him, and he died. Illidan? Maiev and Akama were there too.
You witness all the main turning points of the story, and then one of the established characters steals the spotlight from you. Either you're one of a million nameless "heroes", or you're the fucking messiah along with the other thousand messiahs who usually are even flashier and better geared than you are.
Warhammer does not cheat on you. It is clearly stated: you are the underdog. You are the one who farmed dirt until an hour ago. You're the one that goes on the adventure though, because you're tired of all that shit you had to eat until now. You will probably not survive, and if you do, you even have no guarantees the Graf will agree to reward your efforts.
But when you manage to be the one that stops Heinrich Kemmler, that because of you La Maisontaal is still standing and no army of undead is roaming freely into Bretonnia killing and stealing souls, when you are the one that saves the collective ass of Middenheim nobility from the hands of Chaos, when it's because of you that Bogenhafen is still on the map and it's not a dark maw into the Void, you really get to feel like the hero you wanted to be.
In Warcraft, it's just another tuesday. And someone else gets your glory.