Finally, I've decided to find out just how terrible MG soil really is, and am testing it myself. I'm using MG Potting mix, the kind that "Feeds Up To 3 Months", against Fox Farms soil, which if a 50/50 mix of Ocean Forest and Happy Frog. The only thing added to either of them, is perlite,(approx 25%) so that their drainage qualities are near the same.
I plan to get the verdict, at week 4 of 5 or veg. That should show clearly, which soil is more fertile, or how similar