During Jagr's peak (1995 to 2001), he scored more goals per game in the playoffs than any player in the NHL (minimum 30 games - Jagr played 77), was 7th in assists per game, and 1st in points per game.
Also - during those seven years, when Jagr was on the ice in the playoffs, his team scored 1.51 ES goals for each ES goal against. When Jagr wasn't on the ice, his team scored only 0.76 ES goals for each ES goal against. This means the Penguins were very nearly twice as effective at ES when Jagr was on the ice. Neither Crosby or Ovechkin ever improved their teams to such a large extent in the postseason.
The strike against Jagr is he never had a Smythe worthy run. That's a valid point, but it doesn't change the fact that he was a great playoff performer.