If you are not a mother of a gifted child you will not understand.
You talk about others making judgemental assumptions but then you assume that those of us making comments which you don't like must be making them out of pettiness because we don't have gifted children ourselves. You are mistaken, but not all parents of gifted children will agree on how to handle things.
If your child is academically gifted but socially immature, I would say that putting him up a year is probably the very worst thing you could do. I say this as someone who was offered that option for my sumner-born dd at the end of reception, and considered it very carefully. The thing is, a truly gifted child would need to go up by far more than a year in order to meet their match academically - a year or two ahead is just bright. So the academic benefits are clearly limited unless the child moves up to work alongside a much older age group. However, the child would then be very socially disadvantaged, and for a child who is already socially immature, that would be a recipe for disaster. It would be much better to ask the school to ensure that work is appropriately differentiated - it sounds like they are already doing this. Differentiation generally tends to be quite easy in reception, as most gifted children are self-directed learners and that works really well with the whole "learning through play" approach. Hence my surprise at the teachers having to set him extra work at this stage, but perhaps his lack of social maturity makes him less likely to pursue his natural curiosity? I do think it's much harder for schools to get the differentiation right in the older year groups, when the more formal learning starts, but with the right approach, it can be done.
The reason people are telling you to focus on developing your child's social skills is because, in the longer term, this is what will have a direct impact on his happiness and well-being. It is no fun being a genius if you don't have any friends! And although I hear it a lot, being socially awkward is by no means inevitable for gifted children - on the contrary, some academically gifted children are exceptionally gifted in this area too.
Anyway, you probably don't want to hear it, but it is genuinely well meant when I say that you are not doing your ds any favours if you allow his intelligence to become an excuse for his poor social skills - he needs to learn how to manage his emotional reactions and relate well to other children, and it's your job to help him develop those skills. If he doesn't learn those things, the chances are that he will be miserable and ultimately, his intelligence may be wasted.