I think the reaction to the birdshot strategy is all about being attached to the FBI stopping power model. You see it all the time is science and engineering, people struggle to build a mental model of what is happening and then the model becomes more important than the real experience. Most of us have never shot another person especially if you limit it to handguns. (including me thank god) We naturally hope to extract as much knowledge from those who have or at least have a model to test so that we feel like things are more organized. Throw in marketing hype and subtle changes that are usually improvements and pretty soon it starts to feel like "keeping the faith" is very important.
People collapse thinking about what a LEO should carry and what I have for home defense. I don't think the FBI should do entries with birdshot but given the legal issues and concern for my neighbors I think it is a valid option for my HD.
The more I have read about stopping power the clearer it is that in the end it is shot placement that stops fights. I have a lot of respect for MB and his commitment the the ideas of largest caliber you can get repeated good hits with. Since I don't get to carry here in CA, my thinking is mostly focused on home defense and options for personal defense when TSHTF.
I have settled on #4 shot as my first line HD round for my 12 gauge. I have shot a lot of trap over the years and am fine with being able to deliver the shots. Qt least until I can buy an Abrams tank

Joe
PS why is steel bad, lead good if we have already accepted birdshot vs. buck? Obviously lead is more dense etc. but 1/2 MVsquared = kinetic energy does not care about density.