Injuries really slowed down Jeremy Roenick. You could easily make a claim that he was a top-five forward in the entire league during a three year span between 1992 and 1994. During that period, when he was fully healthy and still wasn't in his prime, Roenick was one of the most explosive forwards I have ever seen. But injuries hit him hard during the first lockout season, and he never was the same. The dead puck era didn't help, either.
Compare that to Leach; I'll admit that Leach could score goals with the best of 'em, but he often was the third best forward on his own line. I'll take Bill Barber or Bobby Clarke over Leach without any hesitation.
The only argument I can make for Leach over Roenick is that the former was a better playoff performer. Even then, I can't agree with that notion. Say all you want about his big mouth, but JR was always a dynamite playoff performer. We all know about Leach's amazing 1976 postseason, but aside from that, he really wasn't an amazing playoff performer. Over 40% of his career playoff goals were scored during that one playoff run. He never again scored at a .50 goal/game rate in the playoffs.
Roenick was more consistently reliable in the playoffs, with less support around him. It's easy to forget about how dominant he was in the 1992 playoffs, when he and Chris Chelios were, literally, Chicago's offense. Played a huge role in 2004 with the Flyers, and obviously, his Game 7 performance in 2008 with the Sharks is the stuff of legends. I believe that JR and Wayne Gretzky are the top two in all-time Game 7 scoring. That speaks volumes about him.