In a pure sword fight? Sauron stomps Gandalf and stomps hard. The only chance Gandalf has is to get lucky enough to cut off Sauron's finger and take away his ring from him.
I'm assuming that Suaron can't use his shockwave and such here and is limited to just swinging his mace.
So based on it being a huge guy with a mace who is slow and lumbering, vs a smaller guy (by comparison) with a sword who is far more agile and would have knowledge that severing the ring would defeat his foe. Why do you think it's a stomp?
He was not hitting every person who flew by his mace. Just those in the general vicinity were killed by the power. Just needs to swing it at Gandalf and there he goes. Dead. Bye bye.
Both sides can use whatever powers aka not other types of sorcery save hand to hand feats. Dalf can lightning zap his sword. This is as fair as it gets.
Yeah, movie version of Sauron was both epic success and epic failure.
On one hand he was smashing aside hordes of 2nd age Elves and Numenorean loyalists with effortless ease.
On the other hand, he was brought low by a hilt shard because Sauron was busy gloating.
Without the book lore, where he immolated Gil-Galad with but a touch, or any of his earlier 2nd age and 1st age feats, Sauron is much much less than what he is in the movies.
Gandalf on the other hand is purely 3rd age, he was not directly involved with the War of Wrath, nor anything up and including the Last Alliance. We do not know how he'd measure up to any of the 1st nor 2nd age powers, and Sauron never directly fought an Istari either. Infact, going purely by movies, Sauron never directly fought a magic user. He did enslave the mind of Saruman while weakened and without the ring, but Saruman was much less than Gandalf the White.
That said, Sauron would also be aware that Whitedalf would know to exploit the severing of the fingers, that and that Dalf is a Maiar as he is, would not take direct chances. He knows better than to underestimate a being of equal knowledge, if not power, having learned the lesson of the sundering of Numenor.
Gahd, so much is missing from the lore and history when the books are removed...