Literally anyone with half a braincell can tell you why Crosby is better than Bossy.
Career points: 1603 points in 1282 games for Crosby, 1126 points in 752 games for Bossy
Major awards: Crosby has 2 Harts, 2 Rosses, 2 Richards, 3 Pearsons, 2 Conn Smythes and 3 cups. Bossy has 1 Calder, 2 Richards (equivalent since the award didn't exist yet), 1 Smythe and 4 cups.
What argument do you even have for Bossy over Crosby? Crosby has longetivity on him. Crosby has individual awards on him. Crosby has production on him (no, playing in the 1980s doesn't by default make someone better than someone who played in the 2000s). Literally all Bossy has on Crosby is PPG (because he played in the 1980s) and cups (because he was on a better team).
And even if you want to look at their stats up to age 30 (pretending Crosby just retired at that point), Crosby's numbers are still better when you take into account leaguewide scoring:
Crosby: 864 games, 411 goals and 1116 points in a league that averaged 5.28 goals/game (1.29 points/game)
Bossy: 752 games, 573 goals and 1126 points in a league that averaged 7.35 goals/game (1.50 points/game)
Bossy produced like 15% more than Crosby despite scoring being 40% higher. And now add on that Bossy didn't play after 30, didn't win as many awards and didn't produce nearly as many total points, and you'd have to be Mike Bossy's family member to argue them over Crosby.
I feel like I'm losing brain cells even entertaining this argument.
Maybe this would hold more weight if Gretzky wasn't beating Bossy by literally 50+ points a season for scoring titles. Saying Bossy was the "second best player after Greztky" is baseless, it's not even clear that he was better than guys like Stastny, Trotier, Dionne or Lafleur. Hell, Lafleur seems pretty clearly better to me.