Happy, I can see that the 'niche' thing is an issue.
As a comparison, DS (good local comp, technically a secondary modern but in fact outperforms our local independents) in addition to sports / PE within school time, plays:
Team sport 1 (summer): 1 lunchtime, 1 after school, 1 good out of school club in the evening (also attended by many children from local independent) per week.
Team sport 2 (mainly winter): 1 weekend afernoon per week all year +1 evening per week for c. half the year.
Individual 'minority' sport 1: 1 lunchtime, 1 good out of school club (2 in the winter) per week.
Individual minority sport 2: 1 after school club run by an excellent out of school provider, who would also provide out o school club opportunities but time is limited by...
Individual instrument tuition: 1 lesson per week out of school.
Orchestra: 1 after school club per week.
Jazz band: 2 evening sessions (same evening) provided at county level
Can't match the concerts and plays - not DS's thing really, though we do attend a few per year.
DD is younger and less eclectic, preferring to spend between 7 and 9 hours per week at a single (outstanding) local dance school (no similar provision in any local independents - good dancers from whom usually transfer to DD's dance school though tend to be at lower grades than those who have been at the dance school from the beginning) on top of individual instrument tuition, rather than doing a wider range of activities, although I suspect when she transfers to secondary her portfolio of activities will widen.
It is harder work sourcing / maintaining all of these as a state school parent, but I suspect that DS at least would do no more at any other type of school, and DD would not receive such high-quality tuition in her chosen area at an independent.