If you playtest and make changes based on the results of your playtesting, you’re no longer following a formula, which is exactly what I was advocating for…
That is not and never has been my stance. I would much rather they have put monster building guidelines in the book. Someone suggested that there not only be monster building guidelines, but that all monsters in the book be built using them, which I think would have boring results. Playtesting, and making changes to monsters based on the results of that playtesting, is important.