The most common element between agnosticism and gnosticism, is that they have a similar name. When it comes to their meaning, they don't really are mentioned closely to one another and certainly not in a dualistic way. So there's something wrong in this reasoning of yours.
Let me start off by saying the syntax in your reponse was a little off. I'm interpreting your arguments the way I believe you intended them, so correct me if there are any misinterpretations. Now that that's been said, gnosticism and agnosticism in terms of their meaning do in fact exist in a dualistic way. The root of both words "gnosis" is latin for "knowledge"-- place the prefix "a" and it becomes "without knowledge", and placed in the context in a discussion on the knowledge of God, those two terms exist in absolute duality. So, I don't see what you could ever mean when you say "they arent mentioned closely and certainly not in a dualistic way".
Secondly the fact that there were even religions centered around the combination of beliefs and knowledge, makes your two-step questioning here not very credible. The two are in practice very difficult to separate and that's the key here: in practice. What you wrote sounds nice and all in theory, but when you put it into practice, it means little to nothing. For example almost any theist by default would be a gnostic theist as when you believe in a god, that's the same thing as saying you know there is a god. There wouldn't be something like an agnostic theist. The only persons who ever would give that answer, would be philosophers and that's because they do what they are supposed to be doing: philosophizing. The main reason why there is such an obsolete option here, is because you were kinda forced to add it.
All you've done is placed my post in a different context and claimed "it means little to nothing in this context". We are in fact dicussing God in a descriptive and theoretical sense, not in a prescriptive or specific sense; it makes no sense to attempt to discredit my post on the basis of religious practicality when the thread was never about prescriptive belief. And the discussion of agnosticism and gnosticism are based in philosophy, not religion.
You also make agnostic theism out to be a "thing of philosophers" when in fact a large quanitity of westerners, mainly Christians, fall into the category of agnostic theist. So, I believe you set yourself up for error when you attempted to put this conversation in the context of religion because belief in God(s) does occur outside of religions and religious practicality. For example, a notable portion of western Christians believe in the Abrahamic God and believe that Jesus Christ is the son of God. They believe in a sense of "faith based belief", but they believe their faith is independent from evidence and reason. They do not know to what extent God exists or if obtaining knowledge of God is truly possible. In practice, they tend to loosely follow Christian tenents such as the 10 commandments and uphold "Christian values", but they are in no way Gnostic.
You're right when you say it's a logical contradiction to claim you believe in God while simultaneously claiming to be unsure of God's existence, but faith exists outside of the realm of logic.
And truthfully it's contradictory. Saying that you believe in god, but don't know if he exists is somehow a valid answer, but saying you're agnostic is not? The meaning of agnosticism is much more complicated than those of theism and atheism exactly due it's relative nature, still you kinda forced it into a strict scheme that suits you. Case and point there is something called apathetic agnosticism, which means you don't give a damn about whether there is a god or not as it wouldn't make any difference. This is something that covers my views much better than anything you listed up.
"Apathetic agnosticism" only expresses your attitude towards and your feeling towards the belief in God, and your "rootin-tootin, no ****s given" attitude does not add or take away anything critical from my post. Before your apathy, you currently either do or do not believe in God, and you either are sure or unsure of Gods existence. Any other nuances like apathy can be stacked upon those two foundational axioms, but the nuances do not discredit the foundation.
You say that answering with "agnostic" is failing to answer the question, but who says the answer is the problem? Did it occur to you that it's simply your question that failed? It's very well a valid answer. It doesn't necessarily make it an elaborate or clear answer, but it's not because you don't like it, it's not valid. Frankly your last sentence made it quite clear that you are forcing answers onto people that you want. When someone replies he's a theist, you know he believes in a god, but that doesn't mean you know which one. Similarly you don't know exactly what someone's beliefs are when he tells you he's agnostic, as it covers a multitude of different ideas, but they all have in common that they don't want to be categorized as either a theist or an atheist, which is a 100% valid answer.
No one is "forcing" anyone into answers. When someone claims that they do not believe in God, and I say they're an atheist, in what way am I forcing them into the answer "atheist"? If you ask me (a man) who I'm sexually attracted to, I say "exclusively women", and you respond by saying, "oh, so you're heterosexual", did you force me into an answer? No. You came to the logical conclusion based on the information you were presented with in my answer. I cannot, then, come back and say "I'm not heterosexual, stop forcing answers on me". Unless I misunderstood the definition of heterosexual or I did not give an answer that correctly reflected my sexual preferences, I am without a doubt heterosexual. No answer forcing involved.
If I'm wrongfully labeling someone, please correct me, but I'd imagine you'd be quite peeved if I or anyoned attempted to claim that they do not believe in God, and are simultaneously not atheists. In the case of Fountain, all the nuances of his belief or lack of belief in God are irrelevant to the question of whether or not he believes or does not believe.
You can't express nuance on something that is not first established, otherwise it's nonsense.
Careful, if you use logic, you're going to confuse him.
Lick the bottom of his boots harder...I think he's almost noticed you.