From the official SW.com databank.
It refers to him as the "Jedi Order's greatest champion". Now one could argue this doesn't refer to skill. However the accolade is contextualized to his lightsaber prowess. In my view it is difficult to read this any other way.
Other skill accolades for Mace:
Mace is referred to as the greatest swordsmen in the order.
"The sight of a purple energy blade on the battlefield means the Jedi Order's greatest swordsman has arrived"
The Brotherhood novel repeatedly affirms Mace as the Order's best duelist, not once or twice but three times:
Mace referred to as the greatest warrior:
Sidious seemingly calling Mace the strongest jedi?
This would presumably put Mace above Yoda and ROTJ Luke in his eyes: