Personally, I think PSE has become too glamorized a term within the hobby. Let's break down PSE shall we and compare it to a real porn scene (or at least what we see). From my recollection of porn, this is how it usually goes (remember there are many variations on the theme). Scene 1: Kissing and disrobing. Scene 2: Girl on knees giving guy BBBJ. Scene 3: Guy returns favor with DATY on girl. Scene 4: BBFS between guy and girl in variations of positions. Scene 5: Return to BBBJ with CIM/facial ending or move onto next scene. Scene 6: More BBFS with guy pulling out as he does cum on body or cum on ass, or a facial. As the session develops it is made clear in the porn that it is 1 shot only and BBFS. So by going by what we see in a porno, PSE should be a non-starter for the hobby because it implies only 1 shot and more importantly the big no-no of BBFS. To me, that's the "by the book" definition of what PSE should be.
As for me, I'm loathe to try and "define" PSE within the hobby because so many see it so many different ways. I think PSE and GFE can coexist within the same session. I really don't believe "specific acts" define PSE. For example, I don't think Greek is a PSE requirement. To me, Greek is more of a fetish. Also, I don't think PSE necessarily means all work and no fun for the provider. I think a gal can have a whale of a time and enjoy PSE just as much as a guy. I also think that a guy would have to work just as hard as the girl to make the experience what it is intended to be. I think those that hit on the emotional angle probably nail it when it comes to differentiating PSE from GFE. I think PSE is more of a raw/animalistic type session. There is no chit/chat or getting to know you. The two just go at it sensually and sexually. It is just pure raw sex for raw sex purposes. One person takes the lead, the other follows and where both people end up defines the session.