Isn't there problems with replacing a single cell causing the battery management system to go whacky? I was under the impression that the cells need to be balanced with each other in some fashion.
Replacing single cells is a problem for other cells in parallel with it, especially with the high current of e-bike batteries, but replacing all cells in parallel (appears to be 4 cells in this battery) should be fine. Either way, being able to replace all the cells at once (worst case) is a pretty big advantage too.
You'll just get less capacity if BMS was wired to monitor individual cells and reported capacity based on that. If you were just measuring voltages at the bus bar, you could over-drain or otherwise over-strain the outlier cell and set it on fire.
Which don't happen often enough to make Amazon do something about fake packs for drills and Dyson vacuums, but I think the chance increases as cell count increases and idiot-proofness decreases.