Appreciated, a sub cell consists of an anode-separator-cathode triplet. All but the smallest cells consist of many paralleled sub cells. It's like that for more than 100 years.
Well, to my knowledge Li-Ion batteries aren't that old...
Important here is that BMS+charger look after the cells, keeping them in their operating envelope and mitigate cell faults.
Yes, but how can a charger/BMS look after the sub-cells?
They have their own social life. The rich feed the poor until dead.