I think that its an ideal opportunity honestly. The skills that this kid could learn would be very valuable down the line not only in getting a summer job when he's old enough but not having to hire a handyman to do household tasks.
Or he could decide he hated it so much he will never pick up another tool in his life and then either always hire someone or let it fall apart if he can't afford it.
That he chooses to waste a valuable opportunity does not negate the fact that it has value. Most kids hate going to school, but I rarely see that being used as a reason not to go.
Deciding that one dislikes a task enough to pay others to do it is not
"wast[ing] a valuable opportunity." That's very judgmental. Also, not every experience of performing a new task is
a "valuable opportunity." Many can be, but if the experience is unpleasant enough to turn someone off from an activity they would otherwise have enjoyed, I'd say it's quite the opposite.
When I had my first car, my older brother offered to walk me through changing the oil. Although I appreciated the offer, I found changing my own oil to be a miserable experience and decided I'd much rather pay for an oil change in the future. As it happened, when the next oil change rolled around, my very kind brother offered to change my oil along with his own, since he didn't mind the task. Afterwards, he said he hated changing the oil on my car due to its design (things he hadn't realized while walking me through the process), and he completely understood my decision to have professional oil changes. In the future when I have a different car, I'll probably try again. But that experience was valuable for only two reasons: A) because I enjoyed spending the time with my brother, who loved teaching his baby sister about cars, and B) it taught me that changing the oil on that car wasn't remotely worth my time and discomfort. Fortunately for me, my brother realized that it was my car
that was the main problem--otherwise, it would probably have turned me off from ever doing my own oil changes again.
The child in the OP apparently didn't enjoy the time spent working with the grandparents, so if the experience does
turn him off from future DIY work, I don't really see how it was particularly valuable. And if the experience was so unpleasant that he's willing to pay to avoid ever doing it again, then I don't see how that implies any fault with the child.