It would not surprise me too much if Jiro's restaurant had only a small edge over the competitors...

While I can't attest to the quality of Jiro's sushi, the quality of the sushi served by a sushi bar at Tsukiji market (you can see the front left facade of the restaurant in the scene where Jiro's son is departing from the market, and the camera is behind him, leaving only his shaded back visible - I can't recall the name) was at least two orders of magnitude* better than any other sushi I have ever had; I have consumed much sushi.

*An order of magnitude here being three octaves of "Mmm!"