Let's assume, although perhaps incorrectly, that said person rolls Nostalrius to PvP, because said person think he/she's awesome.
Here's the problem with BGs. People get carried. During my grind to HWL in Vanilla, we carried one such person who happens to be friends with one of my core pre-made members. There's more of a support system if you screw up. Arena on the other hand, if you mess up, you're more accountable.
In WoD, you have premades going up against premades. You have ranked teams going up against teams of similar rankings. There's an entire system behind PvP. In Vanilla, there is no such thing. WoD PvP is by no means perfect, but it's a much better indication of "skill" than Vanilla.
As much as I want to sit here, beat my chest because I was a High Warlord as well as clearing Naxx40, I can't. What made Vanilla hard, was time and logistics. But high level PvP as well as Mythic raiding is technically harder in WoD.
I don't think many people truly understand what Vanilla was and wasn't. Especially since many players here are in their early 20's. That made them 13/14 years old when Vanilla was actually out.