I am generally of the opinion that Nick Menza and Marty Friedman were the best musicians to ever accompany the Daves, but Dirk's performance in that tiny clip is probably more technically proficient and insane than anything they ever released with Menza.
I honestly found Dystopia pretty average, even if some of the riffing was cool. It was overlong, the lyrics weren't great, Dave's voice is really hurting, and it all sounded pretty similar at a certain point. That said, it's probably a better record than most of their newer stuff.
I think Kiko is fantastic at playing guitar, but maybe a little wanky for Megadeth (I thought the same of Broderick, who just never fit in musically).
IMO, Megadeth is farther past their prime than any of the other bigger four (and that's saying something considering I greatly dislike Slayer and don't give a shit about Anthrax without John Bush).