Nobody can really tell you how you will react to the expansion, that's something only you can accurately predict.
But as far as what I can tell you about Wotlk PvP - It's fast. Both your mistakes and your outplays have a much greater impact than what you're probably used to from MoP because of how fragile players are compared to the numbers they produce, both damage and healing. You can easily get steamrolled because you botched a fake cast and at the same time, you can win the game because you death'd a poly during burst. The damage is even higher on the non-Blackrock Wotlk realms because of bugs and widely spread PvE gear, which sometimes helps mongoloids kill people that know what they're doing simply because their numbers are too high. And yes, Wotlk is one of the expansions that forces you to get PvE gear to stay competitive in PvP because of how easy it is to inflate your damage.
I wouldn't necessarily say it's harder, especially when it comes to BiS geared humans, but if you're not optimized down to the last number then you're definitely going to have to compensate by being better, which in case of Wotlk is luckily completely possible.