Calhoun would definitely go above Izzo and probably Pitino too even if we’re just talking about on-court success since Izzo became a head coach (and obviously if we include his Kentucky stint).
Izzo has had great success over a long period of time and has the national championship, which puts him in pretty select company, perhaps a notch below the true greats but solidly in that second tier, which is still very impressive. Pretty significant what that one championship (or its absence) does to the image - imagine Izzo without his and Ryan or Matta or Beilein with one, for instance.
The question for Izzo in this discussion is whether his physical style impeded further success. Maybe, if you think it made him recruit/play less talented offensive players. But maybe the reason is either his limitations offensively or not getting the top-end talent often enough.
That’s why this year is pretty significant for his legacy in all likelihood. He doesn’t have combos like Bridges and Jackson very often. If he gets that second championship, especially all these years later, it probably puts his whole career in a different light. And he is unlikely to get many better chances.