Arcann was blocking the focus of Valkorion's lightning that was blasting every surrounding ship out of the sky with just it's excess power. He's also more powerful than Vaylin who tore the side off a generator that compares with a large building, and bitchslapped her out of the air despite being greatly wounded and defeated. And yeah, the Outlander thing. Nox or 'Thor both have better feats than Jaina does, and the Wrath and HoT are clearly more powerful than her as well. Arcann's lightning attack he uses in the last fight would also fvck Jaina up something fierce.
The Outlander is easily comparable as a duelist to Jaina. Beating Vong doesn't compare to beating them in the slightest.