No matter how good the BMS is if there is a fault with the cell manufacturing you still have a problem, a quality BMS will shut the whole show down and drain the power in the faulty cell before it heads into thermal runaway. There was an intermittent manufacturing fault with a large production run of LG cells a couple of years ago that were used in Chevy Bolts. Some of them caught fire and GM offered a recall to replace all the battery packs but eventually changed that to installing a better BMS to stop them from catching fire and now they are just replacing the faulty packs, about 1% of the total sold.
