It is not conjecture, it is simple logic.
Here's what you posted that I replied to: "I want the rules to be aligned with the fiction, is because then I can only think about the fiction, and the rules will follow. But if you disassociate them, then you end up thinking about the rules more"
It's an empirical conjecture, about the way some mental and physical processes work, and about the nature of rules.
If character decision and rule decision are associated, then they're just one decision.
Suppose the GM describes a wall. Then the player decides, and declares, that their character climbs the wall. Now, how is that resolved? Suppose that they first ask the GM - "Can I climb the wall?" And then the GM asks what their Climbing rating is. And then the player looks up a number on their PC sheet, and tells the GM. And then the GM tells them to make a roll, and the player rolls a die and then does some arithmetic. And then tells the GM. And then the GM consults a chart or table or other reference, and tells the player what happens next in the fiction.
What I've just described could happen in AD&D (using thief abilities), in more modern D&D, in Rolemaster, in RuneQuest.
Here's an alternative: the GM describes features of the situation, including "Sheer Cliffs d10". The player decides that their PC wants to climb the wall, reviews their PC sheet, and sees their rating Climbing d10. And so the player says to the GM, "I've got Climbing d10, so I'm spending a Plot Point to climb the cliffs". And the GM responds "OK", and then goes on to tell the player what happens next in the fiction.
What I've just described is based on Marvel Heroic RP, but something similar might happen in other RPGs.
The latter approach would be classified as "disassociated" by you and
@Emirikol, as best I can tell. But (i) it doesn't require the player to do anything but play their PC, and (ii) it is more quickly resolved, with less reference to the rules, than the more "simulationist" example.
I've played a
lot of Rolemaster, which is a very simulationist RPG. And it's not a game in which only a little bit of time is spend thinking about the rules and rules elements.
If they're separated, they're two different decisions. Thus in former case you can focus solely on the character perspective, as making decisions as the character automatically makes the rules decisions needed for the play. If they're separated this does not happen. You need to make separate meta decisions regarding the rules.
The two examples I've just posted show that this analysis is not true in general. Perhaps you are contrasting two particular RPGs? I don't know which ones you have in mind.
But it is not a matter of "logic" because "decision" as you use the word is ignoring all the "decision" and cognition involved in rolling dice, doing maths, performing look-ups, and other stuff which happens at the table but has no correlation to anything the PC is doing in the fiction.