I'm not convinced. Spares have been an issue in majority of royal families, and plenty of them raised their children well. It's hard to raise a child is such a dysfunctional vacuum though, where one day they matter and the next they don't, all because of birth order. It's not a slight against anyone's parenting, but if Charlotte and Louis are raised to be working royals, I predict there will be issues in the future. The modern world is not built for a ton of royals anymore.
I respect your view and find sense in it
However IMHO if the spare and heir are raised to know their place and what is expected from them maybe there would not be alot of issue in future (i wont say there will be none though)
And one of the way is give them as you said opportunity to shape their own path in life like having career..i think Netherlands do that just perfectly..