Phil Mickelson has had a Hall of Fame career with 39 PGA Tour Wins and four major championships. He was easily capable of much more.
There have always been golfers who didn't live up to their capabilities. Tommy Bolt, Gene Littler and Lanny Wadkins all should have won multiple majors. Johnny Miller flashed talent to compete with a prime Jack Nicklaus but fizzled out.
The all-time greats have had a number of close calls, but they get excused. Tiger Woods has 14 top five finishes in majors that he didn't win. Jack Nicklaus finished second or third 27 times in majors. Ben Hogan, Arnold Palmer and Tom Watson had numerous close calls. However, they are in such elite company that it's not a case of underachieving.
Fair or unfair, major championships often define the legacy of a golfer.
The list includes enigmatic golfers, consistent winners and flashes in the pan. They all had talent to win more majors.