But I am surprised that welding was deemed simpler. Welding seems to me even more complex than riveting.
It is one thing to be able to swing a hammer, but to do it with force and accuracy when what you are hitting it is not right in front of you and above your head, is quite another task entirely.
I always find infuriating how people under estimate the complexity of doing things professionally. Software developers seem terrible at this even though they really should know better. Everything looks easy under ideal conditions at an abstract level.
I have been raised on a farm when I would be doing a lot of various tasks like that. I observe how people who have not had that kind of experience are absolutely helpless when faced with tasks that require that require to use your hands with strength, dexterity and accuracy. I assume a hundred years ago people would have way more experience than I have.
So when we are talking about people having to be trained, I assume that most of them would already have extensive experience handling a hammer or an ax from early childhood.
It was a unclear example for illustrating learning processes that require physical dexterity and manipulation of materials can actually be more complicated than initially appear.
I was more thinking I can see how you can arrange it so welding would require less of these skills before you can be 'productive'. Alignment tolerance, fitment etc. Getting good welds on the other hand that would pass modern inspection...
Without understanding the actual processes and the expectations of what was required of riveters vs. welders don't feel I can say anything. I think I was more commenting on the grandparents dismissive stance on riveting not being that hard to learn!
I have a similar experience to you also growing up on a farm, and also from watching others learn physical skills when I was working as a carpenter and a little bit of blacksmithing.