George Lucas disagrees with you. Mace Windu won the Lightsaber duel, shatterpoint was key to it. He saw the weaknesses in Sidious' defenses and applied his attack to break them. He also saw Sidious' trust for Anakin, which is one of the reasons he wanted to defeat Sidious quickly.
Mace Windu applied shatterpoint to beat Sidious. He didn't care what effect it had, so long as the Sith were vanquished.
Really? Sidious is alive and Mace is dead doesn't equal a win in most peoples books. Seems to me his shatterpoint failed him.