A few hundred years ago people were completely illiterate
They still are...
They couldn't even read (let alone write), and so what? Complex jobs can be simplified to the point when your average Joe can do them (this is what division of labor basically means). Indeed, the jobs that can be automated will be automated, but the great divide remains unshaken, i.e. some jobs can't be done by robots, as simple as that. Apart from that, what AI are you talking about? This field has been stagnating for over fifty years already. All the recent "advances" have been entirely due to quantitative improvements only (more memory, more processing power, more specialized chips, etc). There is no true artificial intelligence as of yet and may never be (in the sense we think of it), it still essentially comes down to an incredibly complex set of conditions (if-else)
No you can't dumb down complex engineering jobs, it doesnt work like that ,you need brains there which a large part of the population simply doesnt have.
And it's not a question of whether that job an be automated, its a question of time when they will be. Even the engineering jobs can be automated.
Meet engineerbot2.0, I bet he will do calculations much better and with much more precision and care than your average engineer.
It will be like from the movie Terminator, the robot will design a better robot and that will design a better robot.
There will not be much use left for humans, I hope it doesnt end like in the movie but if we want to make use of the robots then we can let them work and we should live off their production.