"The quality required of fuze designs is usually specified by two values: functional re-liability, which ranges typically from 0.95 to 0.99 for complex missile fuzes, and to 0.999 for projectile and bomb contact fuzes; and safety reliability, for which a failure rate not greater than 1 in 106 must be proved prior to release of items for service usage."
https://fas.org/man/dod-101/navy/docs/fun/part14.htm
The reason cluster munitions were banned is that the form factor and econonics lead to less reliable detonation, not because we can't build a reliable fuze, given a larger space and weight budget.