Forgive the NC, but it's v personal, and may seem boasty, but it's not in that spirit at all, honestly.
If he's learnt to work hard, that's all that matters, he will go far. Being comfortable with his success, and genuinely modest is absolutely the best attitude for him, because other children will see through false modesty - their parents may snipe that he wins everything, but they know he's just good at stuff, and is a nice chap with it.
Both DH and I were the ones that won everything at school, all the way through, top in every subject, except sport/games, though we were both on town teams for swimming. I also played 3 instruments, got my Queen's Guide, D of E, and was a cadet sergeant.
We assumed that we were top in every subject purely because we went to pretty poor schools. (I mean bottom 5% in England, not just a bit ropey)
But then we both went to very large sixth form colleges, and were top there too.
Then we went to university, and the work became harder.
DH excelled, and was still top of his year. He had learnt to work very hard as a child, because he arrived in Britain as a small boy with no English whatsoever, was sent to school, and it was sink or swim. He also had dyslexia, which made learning to read and write English doubly hard.
I did nothing. I had never learned to work, because I'd never needed to try at anything before I got to university. I could still get by fairly well, but I underachieved by quite a margin for my ability.
Thankfully my first post-grad job sorted out the working issue, and I've done well in my career (but not without a few "what if"s!)
Our children are following suit.
We put them into a highly academic primary, with super-selective to follow, because we didn't want them to be top in everything (it's a curse not a blessing if no-one else can discuss what you're interested in, if no-one in class can debate and drive learning forward).
One child is driven, works at everything, tries everything at least once, is successful at everything they take up, wins everything- not just in school, but now on a national level too.
The other child (by far the brighter) never works, only does what is fun or of personal interest (will read/research about esoteric things that interest them because that's fun, but never does homework without a huge battle), doesn't care that they're top of the class because it's immaterial to them and will continue to put in the bare minimum because they're still top of the class.
What has been the difference (other than the fact that their personalities are the complete opposite of one another, one introvert, one extrovert) is their peers.
The successful child was in a cohort of first-borns and singletons with extremely pushy parents. For a child with a competitive streak that was a huge impetus. The whole year group was formed of over-achievers.
The one that sits on his laurels is in a weak cohort (weak by the school's usual standard not just weaker than his sibling's year), with many children that are not pushed at all at home, and do not do any extra-curricular activities at all, let alone 'pushy' ones. I know many of the teachers despair of their year (possibly because they're comparing to my eldest's year)
My eldest is far happier outwardly. My youngest is unhappy, but I know feels unfulfilled.
I would say DH is far happier than I am.