In the world of machining people will often build a tool for a job. Its a one off, or something that will rarely if ever be used again.

These features of PHP are still eminently useful if you have to do the dirty one off. You can eliminate a massive amount of time pressure (an emergency or time invested vs time saved) if you dont have a ton of overhead that comes with modern frameworks.

It also allows you to utilize and extend the full http protocol, something which most "serious" frameworks hinder.

PHP doesn't have anything to do with the HTTP protocol, Apache/Nginx/etc handle HTTP and simply call your PHP script with some global variables set to values parsed from the HTTP request

No, but PHP does not get in your way unlike many other web frameworks.

And many of us took the jump and refused to do things that way. You're wrong, PHP scales and you CAN do separation of concerns and have pretty, maintanable code, using a framework or not: just a matter of knowing what you are doing

It's pretty clear that he meant mixing HTML, code, and database queries into a single file was what didn't scale, not PHP itself.

I think you're missing the point of the comment - when it comes to prototyping PHP is incredibly easy to whip out a buggy test thingy in minutes that breaks all best practices but still lets you prove a concept or prep a demo.