A relative has been a roofer for most of his working life (maybe all), which is very long now. There's a talent to it -- a skilled roofer will provide a roof that never leaks, never sags, never loses a shingle to the wind. This relative is such a roofer. It's awful work and he's had multiple serious injuries, but it's still possible to be really good at it.

There's a bit of an art to finishing off drywall and mudding it in to make everything smooth and nice-looking. The difference between somebody who is good at it and amateur work is significant.

This.

As a DIYer for 8 years 'ish, mudding drywall is an art. Where it might take me 4 or 5 (or 6) to get a good finish on joints or corners, it might take a pro 1 or 2 coats and very minimal if not none sanding in between. Primer and 2 coats of paint won't fill in imperfections greater then an 1/16th in diameter so if you have a lot of imperfections, you'll see it in the finished product.

Let's not even discuss mudding ceilings. The amount of upper body strength needed is amazing, let alone good balance on a ladder.

Yup, just because something can be done by a "grunt" does not mean that there isn't skill required to do it well. My girlfriend just moved into a house that can be best described as "the victim of a flip" and you can immediately see the difference between work was done by a pro and someone who is just banging on the keys.

When my dad & I built a house together. We outsourced the drywall and indoor paint job. Drywall is serious detail work, takes too long to get it right if you haven't done it a bunch.