You are misreading perspectives. «The kind of "success" those people are talking about is not becoming an expert»: in the general idea exactly, it is about becoming a
better professional, not just an "older student". And
expertise as a point is there in between: on the one hand the meta-skills and the tricks and the wisdom of those who have been there at different level of specificity, on the other pole your own personal work in a relatively closed frame - the expertise building process takes from both.
In fact, exactly, the answer to King Ptolemy is about the "royal path to geometry", not to "being a geometer". (Already Plato made a notable distinction.)
> they have something useful to say
And in fact "they" do. They (the right ones) can teach metaskills to people who are missing them. (And can people miss them: just yesterday I was treated as a divine helper for having given a relatively trivial advice to strangers passing by.) And said "they" have collected patterns correlated with better professionalism, for sharing: thank you for that, mates.
Sure, "they" may show a high level of genericity: some people sell, some people lead, some people manage, some people assess, some people develop, some people build - nails, chips, fingernail enamel - the advice tends to be universal. But I mentioned Brian Tracy because he openly states as a premise of all his doing that he once was a poor performer in his specific job, he went to the best peer in the firm and asked "how do you do that (of being ten times better than us)", and there were job specific non-trivial attitudinal tricks that the peer shared - enabling him to results.
So, people may have something to teach, and they are frequently open for sharing, and without their input easily some things may stale, and some of them may be critical. (Otherwise, why do you read, if not for refinement? And texts are refined wisdom for transmission.)
> instruction from experts
Not exactly «instruction» but practical or subtle information.
> the question "how to become as good as you are." That's a meta-question that has an obvious answer, which is to study and gain experience in the subjects you want to become good at
No, that is not even valid for a pure theoretician - which in facts studies other theoreticians to squeeze out the teachings. And some of them are written, some are transmitted in presence. This is why we have "schools" instead of just "bibliographies and labs". Your own hard work is just one side, necessary and central - but you do not do it in a jar. You could, but it would take you a lifetime to go there where for the properly guided ones is "past the early stages".
> The problem with that question is that its implication is that there's some special ... shortcut [to] the years of work and study
You have read that implication. It is not necessary. There is no shortcut to the laureate degree. There are shortcuts against reiterating what you always did and was uninformed unwise and inefficient: the others.