Just because Newton published Philosophiæ naturalis principia mathematica in 1687 does't mean that gravity wasn't around from the Big Bang. You could name a "rationalization", and "not a reason", but that, in fact does not stop gravity to function. You can call it whatever you want, even "demon's pull", but that does not mean that you will fly if you jump over a building.
And yes, dissociative mechanics were there always (as I said prior, e.g. character levels), but abstraction is another thing, the exact opposite, in fact. Whereas an abstraction is a mechanical effort to "regulate" some in-world phenomena, a dissociative mechanic is the pull to introduce a mechanical rule into a game, with little if any in-world explanation or later "fluff". When I first read Dragons of a Summer Flame, I truly cannot buy that in-world they use "levels" for the Knights of Takhisis promotions to ranks: it was truly cheesy. "Once a knight reaches fifth level he must endure the Tests of Takhisis". How they even know that they have levels? That concept never was a concern in earlier books, nor it has an in-world explanation.
Yet, you have to remember that this book was released in the dawn of D&D 3rd Edition. They were actively promoting new D&D books and Dragonlance was one of the most succesful franchises, so they forced this component as a sad excuse to promote the game. Before, there was the more blurry, abstract concept of experience, a concept that we can relate to. What level of High School Teacher am I? I don't know. But I have five years worth of experience teaching Literature to teenagers from diverse social classes.
This is an example of how dissociative mechanics work, not originary of your beloved 4th edition. And, as many said earlier, context means a world here. I did not buy that dissociation then, but I nevertheless tried 3rd edition several years later. I tolerate it.
And the fact that there is dissociative mechanics in 4th edition does not mean that all of the mechanics are dissociative. But I do think that there are so much of this, and metagame influences a lot of the players choices, whitout any in-world explanation. And one thing is perception and another thing is phenomena. But actually, I think that in the context of 5th edition, several of the mechanics, implemented in a different way and context, weren't as dissociative, because they were used to reflect some in world phenomena. Vancian combat maneuvers, for example, are now just maneuvers that can be "vancianly pumped up" with some effort by the Battlemaster, as Disarm (see the DMG, if you don't believe me).
You still can disarm a foe, only that not as acuratelly as prior. It is dissociative? Yes, a little bit, but the overwhelming roleplaying focus of the edition worth a little more tolerance, and you easily can relate with a "combat maneuver" passed through generations, although I personally "fix" some of the rules (as the replacing of a meneuver, or other very dissociative mechanics). And the fact that this archetype allows me to play a concept of fighter (my old intelligent crossbowman) that I already tried in previous editions without success has much to do with this. As I said, context means a world here. Dissociative mechanics are one of the many things that we can say that it is present in any edition of D&D, but for many reasons I already detailed earlier, in 4th edition did not work well (at least for me, the tolerance of the mechanics is the subjective value, not their presence).