> Compare this to, say, the bootstrap time for Python or Java
The bootstrap time for a request exists only in a web framework, not in the language. And since you can have the extremes of pure fastcgi or uwsgi, or full Django, you need a more specific comparison.
Java has a high bootstrap time for the JVM. PHP doesn't have that, but the "tear down everything" model might imply a high bootstrap time depending on the framework, because things need to be bootstrapped per request that are already there in Java.
Regarding bootstrap time, have you tried cold PHP, like a cgi script or a PHP script run from shell? Not fast at all. I guess you are comparing PHP with mod_php (or something similar that already has a running interpreter in memory). In that case, it would be fair to compare it against something with JVM in memory, like Tomcat or Jetty.
The bootstrap time for a request exists only in a web framework, not in the language. And since you can have the extremes of pure fastcgi or uwsgi, or full Django, you need a more specific comparison.