I think you've misunderstood the point I was making. I wasn't suggesting that there are no differences in average intelligence between people in different occupations, so I'm not sure how the comparison between 100 oncologists and 100 minimum-wage workers addresses what I actually said.
I was responding specifically to the original wording: "You just wouldn’t be able to get anyone intelligent, hard working etc to do the job if the pay was the same as in the UK." To me, that suggests that people who would be willing to do the same job, in the same location, for a lower salary would, by implication, be less intelligent or hardworking. That's the assumption I was challenging.
I completely accept that an undesirable location may need to offer higher salaries to attract enough qualified people to fill particular roles. But there's an important distinction between how much you need to pay to attract enough people to fill roles and the qualities of the people who would still choose to do those roles for less money.
For example, I wouldn't assume that a teacher working for a relatively low salary in a struggling, deprived school in the US Midwest is less intelligent or hardworking than a teacher at a prestigious private school in New York simply because the latter earns more and is in a more desirable location. The Midwest teacher may actively choose that job because they care about working with disadvantaged children. People choose jobs for all sorts of reasons other than maximising their income.
And this is really my point about the public sector in the UK. It may well struggle to attract enough applicants for some roles because equivalent jobs in the private sector pay more. But that doesn't mean that the people who choose to do those jobs in the public sector are less intelligent or hardworking than the people who choose the better-paid private-sector equivalent. It just means that different people place different values on income, public service, job satisfaction, location, family, work-life balance, etc.
So I think your comparison with minimum-wage workers misses the distinction I'm making. I'm not arguing that occupation has no relationship with intelligence or earnings. I'm saying that salary is not a proxy for intelligence or work ethic when comparing people capable of doing the same job, and that's what I understood the original comment to imply.