want2b I can't think of one practical based subject that requires dedicated study. My father is an engineer who was a visiting professor at Imperial and is still considered a world leading expert in his area. He doesn't have a degree in engineering. He has a degree in economics due to his employer at the time requiring everyone have a degree. He went to night school and worked FT while completing the degree in 2.5 years when he lived in Canada. What he does have is 55 years of experience.
I also know people from my parent's generation who have or had jobs that would requite a degree, and a good one at that now. They're unimpressive and don't seem to know stuff that would seem standard. MIL for instance doesn't know anything about the subjects you would need to get in to study medicine at university, yet reached headteacher level. I dread to think of the number of students who have missed out or wasted years because they have been badly advised on subject choice by her at school.
In the case of your father, I would be wondering whether he could come up with original and complex algorithms relevant to his field, without having studied mathematics for engineering in the precise discipline. It sounds very odd. It wouldn't be possible in my field (law), because the necessary professional discipline to write genuinely innovative academic papers (as opposed to commenting on other people's work) wouldn't be there. Even though in law its considered a plus if you have professional practice before going into academia. In law, it is of course possible to qualify to practice without a university degree, but I have heard it said that such entrants to the profession tend to be "cannon fodder" and lack imagination (I am sure there are great exceptions) and they wouldn't generally be suitable for academia.
In my field, its obvious when people's skills get outdated, and continuing professional education is a must. I find it a bit shocking that people equate working in the professions with simply gaining a degree level qualification and lengthy experience, and not with professional standards such as fiduciary duties.
In the case of your father, it was also the case where he would have had virtually 50% less competition in the job market for his job, as it was much more unusual for the female half of the population to work in his field. In that respect, requiring degrees for jobs removes the jobs for the boys quotient and helps create a more level playing field.