Which is in my opinion a very poor benchmark for RPGs.
In fiction people never fail, unless the failure is required to ultimately succeed. Someone rises to the challenge because in fiction failure is never shown. Yet in RPGs failure must be an option unless you want a very easy game where everyone always succeed. So when failure is a option, either because of realism and/or challenge, you can not simply say that everyone can do everything.
And saying "intelligent people can do everything a bit" is, well, not very intelligent.
Proficiency has not only to do with intelligence but also experience. No matter how intelligent you are, if you, at best, only have theoretical knowledge of how electronics work you will not be able to repair the wiring of a big machine as well as a trained yet less intelligent electrician.
Everyone may be able to fly a shuttle, but how often do you see tactical officers reprogram transporters or analyze anomalies?
I think you forgot the very first sentence from the post you partially quoted.
I don't expect to be GOOD at everything. But in a pinch, lacking an expert to do the job for me, there's a lot of problems I have had to solve outside my professional expertise zone.
So I never said "if you, at best, only have theoretical knowledge of how electronics work you will be able to repair the wiring of a big machine as well as a trained yet less intelligent electrician." for you to need to counter it with "if you, at best, only have theoretical knowledge of how electronics work you will not be able to repair the wiring of a big machine as well as a trained yet less intelligent electrician."
What I am saying is that people tend to be more diverse in their skill sets. I know an MD that programmed his own expert system. I know another that fixed the wiring in his practice's sign because the idiot "export" failed to do it and charged him a ton of money so he figured it out. At this point in my life, I've gotten really good at fixing plumbing, and that's certainly not in my career path.
I do think that there are some limits to these "extra" skills. It's pretty easy for someone like me to fix an electrical system or plumbing system because it's not rocket science. You can stare at the system, think about how it works, then troubleshoot it, and solve the problem, having never done it before because it's well within our mental capacity. It's a key attribute of being a hairless ape.
Problems that are contained inside black boxes are a bit more difficult. If you can't see the guts of a hyperdrive (too small), your going to have a hard time fixing it. this is why modern cars are harder to fix (computers do all the work). Since you can't see the components, you can't decipher it and relate it to any theoretical knowledge as easily.
So in real life, I probably can't build a rocket to the moon (or space for that matter) as I am not a rocket scientist (I ain't that smart). The complexity to the shuttle sitting on a pad is high enough that I can't fathom how all the parts work to fix it if NASA called me up and asked me a swing by and give them a hand.
However, in a sci-fi setting, where everybody's exposed to rocketships (and probably heard their dad talk about exhaust manifolds at dinner because he's a rocketship repairman), the common level of understanding may be higher in that society. So that PC might have a keener grasp of the basics to get started (especially if time is not a concern, or the problem is visually identifiable to an area the PC can focus on).
I don't think a person can be good at everything.
But I do think they can have a broader scope at being functional than most skill-based RPGs grant.
The trick, as I mentioned earlier, is granting enough broadness to allow a "functional" level of skill, while also identifying skill areas that the PC needs to suck at in order to be vulnerable/realistic/balanced.
... But isn't that what the B Ark is for? 
More seriously: The less capable part of humanity will most likely simply be left behind.
