Just want to say it's an absolute travesty that Cito Gaston didn't get in. Won more world series than Leyland, has a better win% and is The first African American manager to win the world series.
I suspect the key difference is that Leyland managed almost 3500 games and Gaston managed 1731.
The only HOF managers near Gaston were Billy Southworth and Frank Selee, and both had career winning percentages near .600 and won 4 and 5 pennants, respectively. Harry Wright too, but that was a very, very different era.
I'm not sure Gaston has a better case than Danny Murtaugh, Al Dark, or Charlie Manual.
I'm not sure I'd support Jim Leyland, either. I don't know that he has a better case than Piniella, or Ralph Houk, Charlie Grimm, Mike Scioscia, or Dave Johnson.