Cell quality is one thing, but it is also possible and necessary to ensure that cell failures do not cause a thermal cascade that causes adjacent cells to fail. The whole "pack caught fire because of one cell" thing is optional. Ideally a catastrophic cell failure results in some venting of gas and a bunch of blown fuses at the cell interconnect level.

The level of increased risk depends on how many cells are in the battery. A large battery will need to be well-protected against cascading thermal runaway, but a battery with 2 or 3 cells there isn't much difference.