Doctor Strange and Vision could be considered exceptions, but when Avengers: Infinity War rolled around, it didn’t matter because Thanos was able to put all six into his Infinity Gauntlet.
He’s the first individual who’s been able to use the Space, Power, Reality, Mind, Time and Soul Stones to their full potential.
As Christopher Markus pointed out in the book Marvel’s Avengers: Infinity War – The Art of the Movie (via Comicbook.com), there have been several instances of folks who’ve wielded just one Infinity Stone not properly harnessing its power.
That’s all well and good for him, but from a storytelling perspective, it paints these characters into a corner.