The Seattle Mariners will retire Randy Johnson’s No. 51 on Saturday before their game against the Kansas City Royals, and the moment deserves to be treated as more than a ceremonial nod to a Hall of Famer. Seattle is giving permanent space to the chapter of Johnson’s career that turned him from a terrifying talent into one of the most dominant pitchers baseball has ever seen. Johnson’s legacy has always been a little more complicated than the average retired-number celebration. He entered the Hall of Fame in 2015 as an Arizona Diamondback, and nobody needs to pretend that was some outrageous injustice. Arizona got an all-time version of Johnson, and history remembers that properly. But Seattle didn’t borrow the Big Unit before he became the Big Unit. Seattle watched the transformation happen in real time. The Mariners had the wildness and the violence. They also had the unfair angles and the flying limbs.…