Sidious wasn't that much better in the force than mace windu was.. Mace windu as well used the dark side of the force, but knew how to control his ability. Windu also had the ability to see exact moments in the future, and use those visions for his benefit in battles. It isn't fair for you to make sidious a far better user in the force than windu, cause if you remember, windu was the grand master of the Jedi order dying the clone wars.