Quality assessment is a big can of worms. Furthermore, who does the quality assessment?
PG does have standards of quality. It's just that the golden-moldies don't meet them -- if these were submitted today they would be rejected. If an old submission doesn't meet current standards of quality, then go fix them, or solicit a volunteer or volunteers to go fix them. Or if a current submission gets accepted [by mistake], but it doesn't meet current standards, then again, go fix it, or solicit volunteers to fix it. Michael solicited volunteers on a number of good books, and encouraged me to do them, even though I was a newbie. Why? Because I was willing to do the work. And why was I willing to do the work? Because Michael had good taste in books. Putting a ton of time and effort into a tiresome book becomes a pain in the behind, in my experience.