As I said, I have handled multiple Glocks that are looser than several M&Ps. Now, I do not have access to 20 M&Ps, I have access to 8. I do not have access to 20 Glocks, I have access to 7.
However, out of the bunch, there are several Glocks that are looser than the majority of the M&Ps, and there are a couple M&Ps that are looser than a few of the Glocks.
Yup. As one would expect, probably more variation within M&Ps and Glocks than there are between M&Ps and Glocks. Generally, blanket statements are misleading if not totally false, even if prefaced with "in general" as evidenced by this thought study:
Population A has an average height of 5'-6" and Population B has an average height of 5'-7" but each population has a standard deviation of 4" Saying "in general, people from Population B are taller" is not necessarily false, but it isn't really useful, either.