There’s one reason many coin collectors get their coins graded with these TPGs. When their heirs don’t know anything about grading, they get, how shall we say it, ducked.
After having only read the first few lines of your post, I can tell you've already learned more about coins than most collectors :-D Did you buy the ANA grading book?
The video in post #7 makes the whole situation a lot clearer. Grading is done to facilitate dealer-to-dealer sight unseen trading. Collectors, by this definition, are an afterthought. A coin that is graded has to meet the standard that a dealer won’t send it back to the dealer who sold it to him. Whether or not a collector might find a coin to be collectable is not part of the equation. It was started by dealers, for dealers. It was not started as a way for a dealer to set a value of a coin for collectors. They state that quite clearly. So, just because I think a coin is incredibly collectable DOES NOT mean that a dealer buying it sight unseen will be happy to get it. They need to rely on buying a resell-able commodity. Maybe the sixth major grading service will be all about the collectors and giving them enough information. In today’s market any coin that might not pass the “dealer to dealer sight unseen” test, can be Detail graded, based on the PCGS video. That creates a secondary market where collectors can treat all Details coins as a big pool, just like existed before authentication, grading, and encapsulation. Maybe they are great, maybe acceptable, maybe dismal. We’re on our own, in that market.