And that's the thing: we're looking at two different versions of "success."
You're talking about a peak, or a small period of greatness. I'm talking about literal DECADES of excellence. Let's not act like Songs in the Key of Life, Talking Book, and Innervisions weren't as influencial to American music either.
On his own, Mike's peak was 82 (Thriller)-87 (Bad). I admit: NO other artist had that type of success as a solo act that could match what Mike did. Thriller is still the highest selling album ever. Bad was literally an album of Top 10 (mostly #1) hits. That's a three-peat, plus the 72-10 season in itself.
But Stevie has been consistently excellent through the 60s, 70, 80s, and even a early part of the 90s.
Greatness is not a race. Whether you do it in 1 year, or 50, it's still greatness. I'd actually argue that the more longer career is admirable, cause we've seen stars burn bright for 1-2 years, and in 5 years, completely fade from the industry. Not to say that was happening with Mike, but Stevie just got a more sustained period of high acclaim for his craft.
And that's what the Mike vs. Kareem debate bases down to: 91-98 (with 94 and half of 95 off) vs. the entire 70s AND 80s.