My non-professional experience is that most people are capable of learning most things with enough time and dedication, up to a certain level of sophistication. There's a huge range of variation in how quickly different people can learn different topics, how capable they are from learning by reading versus listening, how much they struggle with various emotion management problems that might inhibit their otherwise-highly-capable cognitive abilities, et multa alia.

Moreover, very very very few students are ever taught how to study and how to learn. Even fewer still are taught how to understand their own minds, and how to find the balance between training their minds to learn in certain ways and finding learning styles and subject areas that work well with their minds. Some students instinctively realize that writing, drills, and practice form the seeds of intuition, which is the basis for understanding, while others never really figure this out on their own. Some students understand how to take notes that work for them, while others have bad handwriting and find it difficult to take notes at all.

I think that what we tend to perceive as "intelligence" is some combination of "ability to learn a limited set of desirable subjects relatively quickly from conventional instruction techniques and resources" and "well-spoken".

If that is true, then if we want more equitable learning outcomes, we should be focusing on helping students to explore how their own minds work, to learn self-awareness and emotion management skills, to improve communication skills, and to learn their own innate mental strengths and weaknesses, so they can more easily self-select into and self-direct within their own learning environments. And society in general should offer and hold high esteem for a greater variety of learning environments and types of intelligence.

Of course, some people will indeed struggle with emotion management, or communication, just like some people will struggle with learning mathematical proofs or understanding complicated historical events. But I think that's better than our current status quo of just hoping that students figure all this stuff out for themselves. I would even hypothesize that parental involvement in these areas specifically might be causal for some % of differences in student education outcomes.

Edit: All of the above is of course possibly contradicted by the article under discussion here. I'll have to read it in more detail, and maybe I'll update my beliefs as a result.