There's no way Shvedova/Istomin are an easier team than Lisicki/Nielsen. Yari is a much more accomplished doubles player than Lisicki, and in the mixed it is often the female player who makes the difference.
Agreed, and it's not like Nielsen is all of a sudden a brutal force in doubles. Yes, he had a a fairy tale with Marray, but I still consider him as a singles player, and matched up with Istomin, I think there's not much between them on the doubles court. Shvedova's record in doubles speaks for itself, and Lisicki doesn't really have the greatest skill set for doubles matchplay, but the serve is obviously key. When the woman can hold, it goes a long way to deciding sets in mixed doubles.