I think George’s worst decission was not to trust himself enough.

Unlike what most of people think, at times (and only at times) I believe he failed on looking and caring way too much what other people (the industry) was doing when he engaged the prequels. The chosen one thing was taken from Matrix. The Coliseum in AOTC from Gladiator. Qui Gonn came out of someone’s suggestion.

In his initial schemes for TPM back in '97, the Jedi duo was supposed to be ObiWan and a teen Anakin. Had it gone that way without caring about loosing market (sorry, audience) with Matrix or Lord of the Rings, the PT would have turned out a better arc. But from there on, a chain reaction of bad choices took place, of which Jar Jar was just the least important (though perhaps the most evident) of all (if there was no baby Anakin, there was no need of going to Tatooine, or at least not in the same terms where comic releaf was needed to make a light-hearted middle act in a dull desert planet).