I agree with you that it's an educational need - though it's never formally acknowledged as such.
And I agree about how you build resilience (though if all the work is easy, there's no effort to praise and if there's limited scope for exploration and curiosity in amongst the endless worksheets, the journey quickly gets dull).
And I agree with your description of the point of education. Who doesn't think it's about those things?
And (if that's what you're saying) I agree the formal education system starts pointlessly young. FWIW I sent mine to a fully outdoor forest nursery because the traditional nurseries and preschools seemed so schoolified, so young.
I'm really depressed by the implicit judgment and assumptions, that parents like me wrong-headedly see education as a vertical trajectory to accelerate our bright sparks through... or often don't prioritise emotional development in the way the parents of your brother's friend did... or don't understand the value of a "good childhood". Most of us just want our children to be well rounded, resilient and happy, and for them to be appropriately supported in reaching that place.
I don't personally like the word gifted. I think it's unhelpful terminology that glosses over the downsides, sets up straw man arguments about elitism and superiority ("stratosphere" - really??), and creates pressure to achieve "success" and great things in adult working life. (What's wrong with your brother's friend having an ordinary career like his classmates, and how do you measure success and personal fulfilment anyway?) The language of giftedness also seems to have a way of setting folk down a path of pulling other people down, of looking to disprove or discount their whatever-we-call-it-ness. But whatever we do call it, and however imperfect the available quantitative or qualitative measures are, it is a fact that there are a small number of children in whom particular cognitive abilities develop out of sync with age norms, to an unusual and very marked degree. People can argue till the cows come home about what percentage of children we're talking about (1%, 0.5%, 0.1%, 0.001%, whatever) but there definitely are children whose asynchronicity is going to create problems if their needs aren't being met.
And I respectfully disagree that if those children become disaffected at school or hit problems with their motivation or "learning behaviours", we should just attribute it all to innate hardwired laziness/lack of curiosity/lack of bravery on their part. It's pretty shit being bored a lot of the time for years doing unstimulating work at a painfully slow pace, and it's pretty shit not getting to explore issues and questions you're curious about in school. (And they already and inevitably have to cope with the general shit-ness of their brains grasping ideas and complexities that their age-normal emotions totally aren't ready for. And quite possibly also with some degree of unpleasantness or even bullying from certain other children, if they're getting good marks all the time or making geeky or "know-all" contributions in class or group work.) I don't think it's surprising that some children develop anxiety, or stop asking questions, or come to regard their education as pointless, or deliberately underachieve, but I think a lot of that could be mitigated by better meeting their educational need for interest, complexity and appropriate challenge in the first place.