If Windu attempted to defend his allies while fighting Sidious he would over-extend himself and likely get himself killed. Regardless the outcome would have been the same. The first few Jedi were felled simply because they did not react fast enough, no other Jedi accept Yoda and perhaps Kenobi would have fared any better against Sidious Force speed.
By this point Fisto and Windu had gotten their act together and took on Sidious simultaneously, Fisto's more defensive posture allowed him to take the brunt of Sidious' assault and Windu attack him at the same time, but despite this Sidious still managed to kill Fisto.
If what your suggesting happened, Sidious would have fended off Windu while felling the surrounding Jedi one by one, because they simply could not compete with his skill. I also wouldn't attempt to draw comparisons with game mechanics, it doesn't transfer, because Sidious would force the duel on his own terms, not theirs.
No, his Vaapad could reflect Sidious' power, including strength and speed. At the same time the others would attack Sidious when Windu draw his focus. Windu didn't attack Sidious, he chose to dodge, thus gave Sidious the chance to kill Fisto.
It's not a one on one battle, it's teamwork.