[The Saucepan Man]

The quote says that the Isatri were "coeval and equal, doubtless, with Sauron in their beginning, but not more."

Now, of course they were forbidden in their ME forms from using their full Maiar power. And also, Sauron had great armies and servants such as the Nazgul at his disposal, whereas the Istari could only give guidance and direction to the free peoples of ME.

Nevertheless, it seems to me that Gandalf, once he had become White at least, would have given Sauron a run for his money on a one to one. He was, however, constrained from attemting to do so.