Hello,
Yes, because that option “Show current category ancestors” is responsible for only displaying subcategories of that specific current category and it is not responsible for the amount of subcategories.
As I already describes you there is no such option to decrease the amount of subcategories except of deleting them from your dashboard Products >> Categories.
It requires customization to display less amount of subcategories on front end and this is beyond our limitations and support policy.
Best Regards.