I don't think people PL so they can get exp for doing nothing, but so they level up much faster and have to spend less time grinding.
PL is the closest to a golden mean between people who like the grind and those who hate it.
It's not perfect, IMO perfect would be having separate servers for people who don't enjoy timesinks and those who do. Since we don't have that, PL is good enough if only you are willing to tolerate people with different goals and play styles.
