I disagree. Palpatine most ikely would have beaten Windu IF Anakin was not going to arrive. Think about it. Palpatine was manipulating Anakin for years to turn him to the Darkside. He knew the Jedi would come for him. He was ready for the fight. Palpatine was playing Windu, buying time for Anakin to arrive. He needed Anakin there to see what was going on and to give him that final push. That is why he played the weakend old man just as Anakin was rushing to his office.
He didn't lose to Ian McDiarmid. He was about to kill him when Hayden backstabbed him. If that punk weren't there, Mace would've won.
Seriously think about it. Palpatine was doing fine against Windu, then suddenly he is on the ground begging for his life seconds before Anakin shows up. He then plays on Annie's emotions by talking about saving Padme as Windu tries to convince him that Palpatine has to die. It was a setup to push Anakin to the Darkside entirely. Windu was doomed from the start. Palpatine suckered him in. Basically, Windu got got.