Relative Powers

[obloquy]

whether or not Gandalf the White returned to Middle-Earth able to use ANY and ALL of his native Maiarin powers, and chose not to (for whatever reasons),

In order to use all of his powers as a Maia, Gandalf must necessarily be in his natural eala form--or closer to it. All powers of a Maia are not available to them when they are bound to a corporeal form, so unless he was less incarnate as the White, this is not a possibility. I have taken for granted my own belief that Gandalf Incarnate (both Grey and White) has always had the same power accessible to him, and his restraint was voluntary and submissive to the Powers that sent him.