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.