Well, playing Usurper is not as easy as you think. And if the opponent has a well balanced deck they can often win. Synergies, sure, but alot of decks can deal with that in various ways. A synergy strategy is somewhat risky in the first place.
My point is, it does take a good game to win with Usurper as well, as much as any leader. Different decks are strong and weak against different factions/decks etc, that's the nature of the game. Usurper is just one of the many in such a mix.
I'm not a super fan of Usurper or anything, I'm just trying him and finding it fun to be so "sadistic" to my opponents. Usurper makes it about the cards, not the leader, and as such, he is at a disadvantage with 160 provisions.