Look at the stats. Steve Young has more career wins than Alex Smith.
Alex Smith will be remembered as a solid NFL QB, but he has 2 total career playoff wins. There's a reason that he's been traded multiple times.
Compare that number to Steve Young and Jim McMahon who both won Super Bowls. It's not even close in career legacies. Steve Young is in the NFL Hall of Fame and won multiple league MVPs. He is one of the all-time greats in the NFL.