I am an AASP. I replace apple silicon batteries under warranty. They don't require a mail-in. Not sure why his local AASP told him that. I stopped reading after that.
No, it's definitely performed in-house. I can literally see their workshop and talk to the technicians. Not to mention that same-day service would have been very difficult if it were passed off to someone else. And there aren't many AASPs in my town anyway.
As stated in the blog post, my last two MacBook Pro battery replacements, without AppleCare, were $200 not $600, so clearly something has changed.
In the United States?
Which state are you in?