Sombra’s problem right now is that she is good in lower ranks, but not in higher ranks. To rebalance this allow virus to be melee cancelled. This never was a thing, but would give her actual tech/combos which lower ranks would barely to not benefit of, as they generally speaking do not even quick melee.
Then allowing sombra’s ultimate to animation cancel virus & quick melee would allow her to melee ult. This used to be a thing but was shortly removed. (For no reason)
Removing tech (skill ceilling) from heroes is not a good way to rebalance them. Sombra is well balanced right now in lower ranks, because of her low damage and basic abilities.
Rebalancing her further to be worse in lower ranks would be by debuffing the hack cooldown, make this longer and buffing the virus cooldown, make this shorter.