That's often the logic people have that dont have any practical experience as a trained and qualified machinist. There are many people that buy micrometers and calipers from Harbor Freight that have never seen one before and think that just because they bought them, they are qualified to use them. There are many secrets and tricks of the trade that are learned from working in a "real world" environments like engine machine shops. I worked in a top shelf race engine shop for over 15 years. Our customer base was numerous NHRA record holders and drag racing champs who's names would be recognized across the country. So dont underestimate what skillset is held by those that have experience in those fields by over estimating your abilities because you happen to own a mill and lathe. I own those also and have a CNC mill at my home shop also....
Now, I'm not saying you haven't picked up certain skills and knowledge by doing things that you do, but there is a lot that people dont know because certain techniques, skills and knowledge are only gained by working in specialty industries. And even some engine shops have bad practices that may not be considered as acceptable compared to better shops. A lot of our weekly business was spent fixing and redoing other shops bad works....