Yoda was holding back tremendously in both of his fights against Dooku. At the height of his attack, he has creamed Sidious in just three blows:
Yoda redoubled the speed of his blows. Palpatine parried one, then another — and then the red lightsaber spun out of his hands and over the edge. Yoda raised his weapon for the final blow.
-RotS Junior Novel
Why people use Yoda's performance to scale up Zonakin is beyond me.