I understand your reasoning teacher I have a friend with a child who is regarded by all as a genius (maths and music).
In his primary years she stuck with her local state school as they a very average family. They are also black. This mattered to her a lot, in her choice of school, because she flet that no matter how gifted, he was still going to be a black working class teenager in London, and he needed to be able to live that life IYSWIM.
However, state primary admitted defeat very quickly and suggested a selective private school (on a bursary). My firend was very against this as she felt it would make her son an outlier in his own extended family.
I understood this and sympathised, but other matters pushed it forward so off he went (even they found it hard to deal with him, and organised sessions at university as part of his school day).
It hasn't been perfect by any means. But it has been the least worst IYSWIM.
For my DC, it was different. He is not a mathmo. His ability is pretty high across the board. He's not a genius. Other than that he is a perfectly prdinary kid; loves footie, playing on PS3, watching Inbetweeners and eating crisps.
What he needed was an accelerated education across the board, but also lots of sport and banter etc.