The sad thing is, the potential for Sylvansas' character to have a "redemption" arc was their....
...over a decade ago during WotLK.
I know, even back then, Sylvanas wasn't a good person, but she did have a few good moments and hadn't done anything so evil that so as to make redemption seem far fetch. But again, that ship sailed over a decade ago.
Also, it might just be the fact that I'm older, but I swear WoW's dialogue has gotten even cornier over the years. Anduins redemption and breaking of the sword would have been kind of cool if Varyian and Saurfang kept their mouths shut and let their appearance speak for itself.
I mean, I haven't been following WoW outside skimming this thread, but even I knew what was going on just by the visuals alone. All that was needed was maybe a quick "I'm with you, my son" from Varyian and a "Don't give in to this evil, fight!" from Saurfang and that's it, maybe have a few other people close to him show up alongside them (like, maybe, I dunno, his freaking mom for starters?), not saying anything, but having their mere presence alone add weight to the scene.
The fact that they talk throughout the whole damn thing leads me to believe they lacked confidance that the scene could speak for itself.