It's not debatable yet, Painter has better conference records than both over the last 5 years. Arbitrary number I know, but consider this. Over the last 10 years Beilein has a 59% conference record, Izzo has a 70% conference record and Painter has a 66% conference record. This includes an 8-10 and 5-13 conf record for Painter. Over the last 5 years Beilein has a 61% conference record, Izzo has a 73% conference record and Painter has a 75% conference record. So the 5 and 10 year trends show that Beilein and Izzo, although improved their 5 year trend over the 10 year, they are both only 2-3% better over that time. Painter jumped 9%. This is a tad deceiving because the two year blip makes his improvement look much higher. So let's take out those two years and insert the two years just prior to the slump. Again, this is very arbitrary but an exercise worth looking at. So the 10 year trend for Painter minus the two down years and adding the very two years prior (so 12 years minus the 2 slump years) his conference record is 73%. That's better than Izzo's 10 year record.
Now, I know you are going to make a bunch of arguments against what I just did, and honestly you should have some good arguments. What I was trying to demonstrate here is that Painter is a better coach than you are giving him credit for and I think you are making NCAA tourney successes your primary factor. Which as I stated before, Izzo and Beilein get higher rated recruits and are very key to tourney success, besides the occasional outlier. This should also be a good argument that Painter is actually a very good coach, pretty much on par with the other two (besides recruiting obviously).