While your statement contains some truth, it's not the most helpful way to say it. Grind isn't the end all but it certainly has a measurable impact on the speed of conversion and the allowable speed of sparging. In case that's not clear, a coarse crush takes longer to convert because it takes long to hydrate. A coarse crush requires a slower fly sparge because diffusion out of the core of larger particles just takes longer. We can debate a bit about how much of the overall conversion picture is impacted by crush, but it would be absolutely false to say that it doesn't matter.
Also, silver bullet? When I read the thread it looks like a bunch of people trying to be helpful and brainstorm all the reasons why efficiency may be low.
Temp
Time
Crush
pH
Total Diastatic Power
Those all factor in to conversion and many of them are interdependent. To troubleshoot conversion, you have to measure wort gravity directly out of the mash before sparging.
Once you collect all your wort in the kettle you can measure lauter efficiency.
Finally when the wort is in the fermenter, you can measure brewhouse efficiency.
In my opinion, the low efficiency was likely a combination of many factors. At 150F, a slight mis-calibration of the thermometer reading high would slow conversion down quite a bit. If the grain crush was coarse, it would be even worse. Couple that with a relatively low diastatic power of the total mash with the higher percentage of adjunct, I'm not surprised. Without measuring gravity in the mash directly, we can't separate out conversion and lauter technique effects.
