Following that premise, then, what is the core defining trait of 4E? Is it the choices? The grid? The unified resource structure? What do you consider to be the essence of 4E, such that you would recognize a game as being 4E-derived if it shared such an element?
So even though this discussion has gone off track, I think the original question is an interesting one and I want to answer it
It's a really good question. My primary group liked 4e quite a bit and they don't care for 5e much at all, so to find that essence I'd think about why they like 4e but never want to play 3e again and are at best mildly negative to 5e:
1) Big Damn Heroes. This is probably the biggest one. They like that the default for the game is not "zero to hero" but "hero to superhero". Personally I think that's a big defining trait for 4e, and I also personally think its at the root for a lot of the hate that the edition received (and continues to receive even though it's now long out of print) because for a LOT of people "zero to hero" IS the game.
2) "Per encounter" vs. "Daily" resource refreshes. And where it is "daily" its for something really cool and not just a magic missile. They all really liked this aspect of the game - especially going into combats at full hit points every time as a "standard" way of doing things.
3) Abilities to help visualize what they're doing in combat. They all liked having At-will and Encounter powers as inspiration for describing how their actions looked in combat (when you're on you can come up with flashy descriptions without prompts - when you're off, the prompts help with not having to say "I guess I swing my sword again" for the umpteenth time).
And to add my own as a GM:
4) Organization - putting all of the rules for adjudicating monsters directly into the statblock makes running creatures a breeze. I miss running 4e every time I see a spell ability listed on a creature in the MM and I can't remember off the top of my head how the spell works.
5) Improvisation. This ties into monster organization, but in general I found 4e to be the easiest official edition to run combat encounters "off the cuff" with no prep at all (Dungeon World has this beat, but Dungeon World is a collaborative improv game that's built for no prep games so it's in a different category imo). The monster math is open and obvious, so once you know how it works it's pretty easy to just come up with stats on the fly if you need them. Or if you want to run straight out of the MM the stats are all there without having to cross-reference any other books. And since the game is built (mostly) around a per encounter balance it's actually pretty easy to build encounters that don't accidentally overwhelm or underwhelm the PCs.
I think those are the things that my players would say are the "essence" of 4e to them. Probably why we're enthusiastically playing 13th age these days - it's got a lot of similar "essence" along those 5 points, despite being a pretty different game from 4e in a lot of other ways.