My view of a successful MBB coach is one who can consistently field a team that wins the Summit Conference perhaps 2 out of every 5 years, with the other 3 years still in the upper half with maybe a random NIT bid. This also includes beating 2/3 of the Dakota schools each year. I don't expect MBB to be #1 every year, just not be a basement dweller. A cherry on top would be one first-round win in the Big Dance once in the five-year cycle.
Maybe it is too high of an expectation, but don't think it is an unreasonable one.