no one gets past 0/6 without starting a chat war, or being drag in one
This is not always true. And if it is true in this particular game, you can report him for flame instead. Seeng all that "wtf i got banned after 1 game" threads here, this can end in same ban you want him to get.
if shes 0/9 I doubt her adc would be smth like 15/4
Most adcs dont really need snowball like 15/4 to function
enemy adc wouldnt just one shot any possible carry before leona even cast her ult or miss the E and get melted in 2 seconds
Thats one possible outcome. Another possible outcome is: enemy 15/4 adc carelessly walks in range of Leona's E, gets EQR chainstunned, while you(the one who didn't die 9 times) use this time to kill him(as adcs are usually squishy even with item advantage), get a bounty and win the fight.
Its not 100% chance, and not even 50%, but its still better than 0