Only skim-read the thread, so apologies.
When I was younger I never did any extra-curricular activities until I was secondary age. Very few people did, in all honesty. I did gymnastics, but was too old by this time to realise any potential, and karate, which I did excel at. I gained so many friends and skills from my activities and it is something that I cherish from my childhood.
When DD was 4 we started her on gymnastics and swimming. As parents, we did this because she is, and was always, academically very able, but her physical skills were playing catch-up.
She's now 7 and in swimming is ASA stage 8. In gymnastics, she has just been selected for squad.
She enjoys her activities and, not only has it helped her physically (she is also asthmatic, so regular exercise is important), she has group of friends that are separate to her school.
If she asked to stop one or other activity (or both) tomorrow, I would do, but she loves swimming an gymnastics too much to stop at the moment.