sorry bro you gotta ks to get S and u also have to farm ur adc's minions. Sorry brah you lose.
But in all seriousness, 12 deaths is too many. That bard also had higher kill participation than u and a better ratio.
S goes off all things, if you focused on attempting to live more (yes you did well but... could you have done better?) that is what the algorithm is looking for. I bet you could do even better with kayle support she has amazing potential.
All in all it measures your stats against what other people in the region (other kayle supports specifically) do with that champion. Therefore, if you had died less, you would have gotten a higher score.