I agree with most of what you've said here. A generic occupation such as "physicist" or "programmer" allows for a broad array of possibilities, many of which don't require more than ~100 in IQ. For example, making Excel spreadsheets to convert test grades into a final grade is quite easy, despite technically being "programming". A huge contrast is found when comparing that with writing a 3D or physics engine. The difference in IQ requirement could be 85 versus 125. My hypothetical scenario were better with a more specific occupation, having a higher requirement, but I didn't find any better data than that on the link I posted.
An important factor to consider with all this is the rate with which a particular person could learn or carry out such a job's activities. There is a reason why retarded people (IQ < 70) are called "slow", and that's because they learn at a much slower rate compared to persons of 100 IQ. If you tried hard enough, you could probably get a person of 70 IQ to remember some physics equations, but (a) it would take a really long time, (b) they would not truly comprehend the nature or derivations of the equations, and (c) they would probably be very poor at recognising when to apply a given equation, let along actually applying it. The point is, they would be completely unable to compete in the job market. And this phenomenon is by no means exclusive to "retards". There are many concepts for which a person of average intelligence would seem retarded at trying to understand, and this could probably apply to persons at any level of intelligence.
A final note is that job requirements, both in terms of education and intelligence, are always changing. Due to advances in technology, some jobs are far easier than they used to be, while others have become much more intellectually demanding. Programming, for example, is much easier than it used to be -- as a result of new IDEs, new programming languages, and more system resources. On the other hand, I imagine being an auto mechanic requires more brains now than in the past. Generally speaking, the easier the task or job is (intellectually), the more likely it is to be replaced by automation and or robotics.