here is my problem with that. mace is not one toy "play with his food"
He's a man of action, if he was so much stronger, why did he not simply cut Sidious down earlier? why did he ask for anakin's help when he sowhed up if he did not need it?
also, even if mace is using Vapadd, a dark side style of fighting, he's only playing with it, Sidious has dedicated his entire life to the study of the dark side of the force. he would, therefore have more knowledge of it, in therory, making him stronger in it.
Now, it is estabilshed that mace is one of the greatest jedi swordsmen of all time, but palpatine had no trouble keeping up with him in the fight, untill he was disarmed. Most likely, palpatine cheated, but even then, as we've said, he was a master at adapting to the situation. He drew on the darkside, and kept pace with mace, waiting for the key moment when Anakin would arive.