I agree. I think many people are thinking the main obstacle here is the mathematical mistake, when the main obstacle here seems to be explaining the mathematical mistake to 4th graders who are learning fractions for the first time. I'm also not sure what the best way to do that would be. If you start with one type of fraction (say, half circles), it's probably easier to intuit things like 5 halves and how much that is, but other things are probably going to be more difficult.
So yes, telling kids that there are more complications when approaching certain problems that you can explain later might be a good approach.
I have a PhD in physics and the more I think about that, the less obvious it becomes (or at least makes you seriously think about it).
The average person is probably in the easiest situation because they learned how to add fractions without further philosophy and they can live happily after.
So yes, telling kids that there are more complications when approaching certain problems that you can explain later might be a good approach.