One one hand, if jarjar is just a dumass, it means that palpatine's rise to power and the creation of the clone army are just the result of an impredictable blunder.

On the other hand, if he is indeed a sith, it means that his presence at the senate in ep. 2 was engineered from the start with palpatine (ie : having padme go back to naboo early in ep. 2, etc.).

As ****** as it may be, I think having jarjar as the ultimate villain just makes sense. If not, why did he appear in ep. 2 at all ??

The actual surprise is that Jar Jar Bings will be revealed as a sith.
Remember that :
- he came out of nowhere in ep. 1;
- it was never really cleared out why he was cast out of the gungan city;
- more importantly, he is the one who proposes emergency powers for palpatine in ep. 2 and provokes the creation of the clone army contrary to the will of padme, who is strongly against it.

My guess is either he was a sith from the beginning or he was replaced by a shapechanger between ep. 1 and 2.