@blackmageleo: In general they are, but a few magic users who are neither are of comparable power levels. Namely, Teclis, Caledor the Dragontamer, and Nagash.
It might be prudent to specify why you think Sauron is superior to a Balrog. Simply saying so will not likely convince most.
You claim that Tolkien put Sauron above Gandalf and Saruman, but I do not see a cited quote for this assertion, only a link to Gandalf's RT.
Additional evidence of Sauron being above Gandalf and Saruman: Movie-Canon Gandalf, who was forbidden from challenging Sauron directly, could contend with Saruman in his Gray form and basically one-shot him in his White form. In conjunction with Sauron beating Gandalf the Gray as the Necromancer, it can be reasonably inferred that Sauron at his best is superior to Saruman and both iterations of Gandalf (at least in the movie canon). You could go even further and highlight the Witch-King challenging Gandalf the White in the movie canon. Since it makes no sense for Sauron at his best to be weaker than his Nazgul, this further suggests his being above Gandalf the White.
I vaguely remember it being claimed that Tolkien once claimed Sauron at his best was superior to Morgoth during the War of Jewels. Now I have no idea if Tolkien ever said that or not, but if it could be proven, it would be a good accolade.
Helped the Balrogs liberate Morgoth from Ungoliant's clutches. Given that Morgoth summoned his Balrogs to him with a magic shout and they covered an incredible distance in a short span of time, superhuman travel speed can be assumed from this.
For SoM/SoW Sauron, he contended with Talion twice, both times without his One Ring and presumably not at peak power. Especially impressive given that Talion by the end of SoW had fought and beaten multiple Nazgul one on one, including the Witch-King himself.
You might mention that he factually killed Gil-Gilad and Elrond. One-shots the latter in the movie continuity despite his being capable of fighting through endless Orcs for days without rest.*
* Guide to Weapons and Warfare, which I consider a supplement to the Movie Canon, explicitly says that the Battle of the Last Alliance goes on for several days, and there's no reason to think the Orcs would just let the men and Elves take a rest out of chivalry (something Tolkien Orcs have none of).
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