It's far too easy to get lost in the weeds with specific examples which are always biased towards "proving" a particular point. I have been quite clear about my views on this and I don't think I need to explain further. If you cannot or will not play the character in front of you or at the very least, make an earnest attempt to do so, then you are not particularly welcome at my table. Is emptying a cart to make it lighter an earnest attempt to play your character? Then it is probably fine. OTOH, is the reason your character has an 8 Str and 8 Int because you are pretty obviously min/maxing your character because you think that you can do an end run around the skill system by playing "smart"? Then, well, there's the door.
The problem with this is that it is a standard trope of fiction that characters which aren't particularly clever often think of clever plans by doing the simple obvious thing that the more clever character didn't think of. This is the "kids say the darndest things" trope and related tropes. So there is nothing particularly wrong with a player who is intelligent, playing a mechanically "dumb" character in a "Forest Gump" like manner where he solves problems despite his lack of intelligence rather than because of it. Yes, there are artful ways to play this out and less artful ways of playing this out, but I'm not going to show someone the door simply because they aren't an artful enough of a thespian for my tastes.
What are you going to do, tell the player that their character is too dumb to have come up with this plan? Force the player to make an intelligence check to come up with the plan? Are you also going to make the 18 INT character make an intelligence check to come up with the plan? Because if you are going to do that sort of thing, why allow players to play their characters at all?
If a player dump stats an attribute and in your opinion doesn't suffer enough of a penalty for it, then it suggests that attribute doesn't actually have enough impact on play and possibly should be removed from the game entirely. If it really was the case that there was no mechanical penalty for low INT, why do characters and the rules system have INT at all? That sounds like a problem with the system and not with the players.
So, to be perfectly clear. Play the character you brought to the table. Sure, you can try to engage in a social challenge, go right ahead. BUT, know that you will very likely fail difficult challenges regardless of what approach you use.
This is where I'm having the hardest time understanding your point of view. I don't think anyone has argued that for example in a social challenge you ought to succeed in difficult challenges regardless of your characters social skills. I think that regardless of the approach that a player takes for solving the problem, having high skill in social conflicts is going to make you much more likely to succeed. All people are suggesting is that approach does matter, in the same way that kicking down the door might be easier than picking the lock, or conversely the door might not even be locked and so opening it is easier than kicking it down.
I already know you and I have different processes of play, but typically what I'll do in a social encounters is allow the player a little bit to role play their character and then once I think they've reached a good point in the role play, I'll ask for a social check appropriate to their role play - intimidation if they were threatening, bluff if they were manipulative, diplomacy if they were trying to be persuasive. I'll apply a circumstance bonus based on how appropriate their argument was, whether they raised salient points, and how entertaining their role-play was (which means that if they are 8 INT and they played like their INT didn't matter and used a lot of big words and complex idea, I might penalize them). Then they have to roll. Success is far from guaranteed. If you are playing a misanthrope vermin sorcerer with multiple bloodline mutations, chances are you aren't going to succeed at anything regardless of what you role played. People are going to be too freaked out to even pay attention to you, and regardless of how apt you thought your language, what people heard is going to be uncanny and alien.
What I tell players is that what they hear as players in their own words isn't what the NPCs necessarily hear. I have a player who is socially awkward and stutters a lot when he tries to RP. Yet his character has very high diplomacy. Consequently, while the player may stutter and be awkward, the character doesn't. If the message is on point, the character will deliver it with the eloquence the player lacks. Conversely, if I had a player that is very eloquent, but has large charisma penalties, the character will deliver the message in a wholly awkward fashion. The player has in fact played out that trope scene from so many movies and TV shows where a character tries to achieve some brilliant oratory, but what has come out of there mouth has in fact made a fool of them.
Because, at my table, you are going to roll BEFORE you narrate.
Fortune at the beginning is a perfectly valid approach.
But my problem with it compared to fortune in the middle or even fortune in the end is that it tends to make the narration irrelevant and anticlimactic. There is a tendency that if the roll actually is everything and is all of the deciding factor for the narration to be deprecated and not really happen, because why bother? The results are known. Perhaps one sentence will be said to humorously explain the result of the roll, but since the narration adds nothing there is no more reason to do it than there typically is reason to narrate the specifics of what happens when someone swings a sword.
Point that I want to convey though is that just because you use Fortune in the Middle or Fortune at the End doesn't mean that the dice don't determine what happens and that you can make an end run around a games mechanics.
And the other point that I disagree with you over is that just because you have dump stated something doesn't mean that the proper way to play your character is failure.