Zebramummy, I don't think there is anything wrong in seeing yourself as your child's main educator. I probably do the same, though I have the deepest respect for their teachers: it's just that I'm going to be around for longer than them, so am likely to be a more lasting influence.
What I have learnt over the years though is that my ability or right to influence what my children become is still limited. I can try to make them interested in the things I love and it's a great thing when it works. Dd and I spend hours discussing books and historical events and this is one of my greatest pleasures in life.
But I cannot make them talented if they are not, and I have to remain open to the fact that they may develop talents or deep interests which are not the same as mine. And then it is my duty to support them in that rather than trying to make them become what I was at their age.
My ds (9) is showing no interest at all in literature or learning languages, which was all I thought about at his age. I was top of my year, he is in the bottom sets, because that is who he is- essentially, he is not me. Instead, he has an interest and (I think) a talent for drawing, which is something I have never been interested in myself. So I can choose whether to be disappointed because he can't do what I can, or proud and delighted because he can do something I can't.
Imo my job as an educator is not to make him think that he should be like me, but to enable him to enjoy who he is.
At ds' age, I had relatively little interest in music which was my mother's greatest love and the thing she felt she had never been allowed to develop to her fullest potential. She wisely settled for some kind of halfway house: she let me do enough music to gain a general idea, but did not leave me with a feeling that I was expected to excell because she had. If she had pushed it more, I could have ended up hating music for life; instead, I can quite enjoy going to a concert, though I am not a performer. And I am not left with the feeling that I was not allowed to be myself as a child, because somebody else's ideas of who I should be got in the way.
I know this is not what you asked for: you wanted practical guidance on how you can make your ds develop quicker and be talented at art. And we cannot offer you that. We cannot even know if he has any talent. And we do know, from our own experience, that pushing a child to develop faster than he is, can be potentially damaging.
What you can do is make sure that art remains fun and non-pressurised for him. And if you want him to make the most of his time at school, then it would probably help if you could respect his teachers as people who are working for essentially the same goals as you- if he picks up on your negative attitude, he will not get much benefit from the time he spends in school.
I am far more educated than any teacher dcs have had to date: I have read more, I speak more languages, I could spend my time picking holes in what they do. Instead, I have come to recognise that through their daily experiences in the classroom, they have gained knowledge that I do not have. We complement each other, it works well. I respect the knowledge and experience they do have, and I hope they respect me and my children.