IQ measures things like innate problem-solving ability, processing speed, and ability to retain and manipulate information in working memory. (I don't like the term "gifted" personally, and there's a lot of baggage around it - high learning potential or exceptionally able are alternatives.)
So yes, creative thinking and curiosity and (depending on personality) initiative and being a self starter are in the mix.
These are all fine qualities, for a toddler starting to explore the world, or an adult in the workplace. But please consider how that plays out in a school classroom for HLP kids.
When your numerate 5 year old says "no thank you" to the activity using counters to work out 1 more or less than, for numbers up to 10, and - being as you say a self-starter with lots of initiative and creative solutions - quietly fecks off to find himself something more useful and interesting to get on with, we typically call that being naughty, and not following instructions, and having poor listening skills. We also call it a safeguarding incident if the little s**t managed to hop the fence in the process of going self-employed... So, going forward, do we just bring the behaviour policy to bear and put him On The Cloud and keep him in at playtime until he becomes more compliant, perhaps with some ELSA support for those lagging listening skills....or do we also afford (appropriate) outlets for self-led learning and for his creativity and initiative, and differentiate the maths work for him (ie support for his HLP needs - which you say he shouldn't need?).
Rinse and repeat the former approach, changing the factual matrix according to age, through the school years, and depending on personality and circumstances the outcomes may be suboptimal. I don't have stats to hand but anecdotally, I know of a child who became the class clown and channelled their many talents into disruption instead of their learning; who turned things in on themselves, became depressed and disengaged and flunked GCSEs; one who truanted, had multiple exclusions and ended up in a pupil referral unit; one who sadly fell into addiction and suicide. This population has been shown to be over represented in the teenage suicide statistics and the youth offending rates.
Less dramatically, it's very very common for these children not to learn useful study skills or how to fail because they're never challenged, and to be perfectionists used to high marks, and so to have a catastrophic mental health crisis/breakdown when they finally encounter stretching work, whether that's in year 11 or at A level or uni or in the workplace.
I don't think it's fair to look at these outcomes and say, well they weren't really gifted then or they'd have been self-starters and done better for themselves
As adults, these children will have agency to choose their own work and careers, to pursue their interests and use their abilities as they wish to, free of the constraints of the school timetable and the National Curriculum. And they will no longer be grappling with asynchronous development, with cognitive abilities that are beyond their physical and emotional ages and the daily challenges that creates, and will be more comfortable in their own skins. So no, of course they don't need "lifelong support to function" and live happy and fulfilled adult lives, if they make it there well-rounded and resilient. But they deserve and need our understanding and appropriate help through the school years in order to get to that point. Sadly, many don't get that.