Difficulty is subjective. Like yeah, to me and most people the jobs labelled “unskilled labour” are going to be easy and being a doctor or dentist is going to be hard, nobody’s arguin that. But it gets a lot fuzzier when you start getting into seemingly low-skilled jobs which are put at higher value and labelled “skilled labor”, and seemingly high-skilled jobs which are put at lower value and labelled “unskilled labor”. This is especially apparent with manual labor (including some trades).

Plus it completely ignores the fact that things that are hard to one person can come extremely easily to another, and vice versa. Not every fast food employee can be a lawyer, but not every lawyer can be a fast food employee. Surprisingly, employers for “low-skill” jobs can be very picky with employees. And there exists extremely low-skill lawyers just like there exist extremely low-skill fast food employees. Same with teachers. The only difference in this case is that being a lawyer requires you to pay tens to hundreds of thousands for a degree, so the barrier for entry is artificially higher for poorer people.

Right now the case is mostly just that jobs considered low-value by society are called “unskilled labor” while jobs considered high-value by society are called “skilled labor” despite not being higher in actual skill used or required. Even disregarding manual labor, I wouldn’t consider my office job particularly high skill, it has a low barrier to entry and anyone could reasonably get a similar position with very little time investment, but it’s lumped into “skilled labor” just because it pays a lot and people don’t view it with a stigma like they do with low-paying jobs. Hell a lot of middle managers know absolutely nothing about the job of the people they manage, but they get labelled as “skilled laborers” anyways.

You are confusing line cooks with dishwashers. No one hires a line cook that has no experience or training.