It's amazing that you're the one saying that "average" people cannot, in principle, understand some things, yet you're calling me arrogant. What you're saying is absurd. It's a matter of interest, pure and simple. IQ is testing for very specific things, and those who are interested in those types of things, language, math, patterns, etc, score higher. Those who aren't interested in those things score lower, and tend to always score lower because they never become interested enough to learn them. Rarely is someone truly passionate about mathematics but unable to learn it because of some fundamental limitation. The only people that applies to are those who are cognitively limited in severe ways that prevent them from learning. The fact is, people you so easily dismiss as being innately stupid, just aren't interested in intellectual pursuits, which unfortunately is extremely common in our civilization. Even those with slight cognitive disabilities could get a PhD at MIT if they were extremely interested in doing so, and had the lifespan it would take to learn it at their much slower pace. Most people like that aren't interested at all in intellectual pursuits, because of culture, but also because, with it taking so much longer to learn things, it's just not fun.

Also, it's important to note, a lower qualitative level of intelligence can't recognize a greater intelligence. For example, my pet cat doesn't realize I'm smarter than it (in fact I have a feeling it assumes the opposite lol). But there is no higher qualitative level than us. That's really the main point, there is no higher than universal. There could be much greater quantitative intelligences than us, but we would definitely recognize that. It would just be an entity with massive creative ability, but they would still be able to explain everything to us, and even without them explaining it, if we took the time we could understand it ourselves.

So when I said "mentally disabled" in that context, I meant severely. As in, needs round the clock care. People with functional intellectual disabilities still have universal intelligence, it's just hindered to whatever extent. The evidence is the mechanism of explanation and computation. If someone can understand anything beyond the genetic knowledge they're born with, then there is nothing, in principle, preventing them from understanding anything else, regardless of its complexity. The difference between a very simple explanation, and the most complex explanation, is the length of the string of statements that explain it. As I said before, there are of course some explanations that require some base level of memory to understand. For example, to truly understand it you must be able to hold a certain level of information in your mind at once. I grant that it's possible a person with disabilities lacks that memory requirement, but even in those people, universality is still there. They have the qualitative requirement of universality, but lack the quantitative requirement of memory. I also grant that there could be explanations that would require quantitative increases that we are incapable of in our current state.

But in both cases, we can make quantitative increases with the requisite knowledge. In fact, we already do. We use computers all the time to gain major quantitative increases in processing power (speed) and memory. We even use simple paper and pen to do this. The proof to Fermat's Last Theorem is far far too long to hold in our mind at once, and even the mathematician who crafted it had to write it out as he went along, continuously going back to previous sections to revisit his conceptual building blocks. Yet it would be foolish to say he doesn't understand it just because he can't hold the entire thing in his mind at once. In the far future, we'll be able to add more and more processing power and memory to ourselves, perhaps even more efficient algorithms, but we'll never need to (or be able to) increase our intelligence qualitatively. Universal is infinite in it's capacity to understand, and you can't add to infinity. If you can, in principle, fully understand anything, then there's no way to fully understand anything in a bigger way. Anything means anything.

You took the words right out of my mouth, any conscious Intelligence would see itself as general intelligence because of the barriers it can’t look past. It seems it would be much more likely that there are a multitude of higher levels, each with their own emergent properties.

The vast majority of people don't have the knowledge needed, explicit and inexplicit, nor the interest, to get a PhD at MIT. But their brains and minds are absolutely capable of learning and retaining the necessary knowledge to do so. It's absurd to think otherwise, not to mention sad.