how often do you play adc? its not always the adc fault if they get killed. especially if the enemy team decides they must be targetted, because they are fed. often there jsut isnt crap u can do about that as adc. split pushing can be totally reasonable also. this game is not all about kdr. if your team is behind then split pushing might help stall the game and give people time to catch up.
usually the biggest reason u lose game even when winning laning phase is because people dont think about objectives. especially the top laner or jungler or someone trying to be an amazing 'carry' who jsut does nothing but farm and roam, getting great kdr by picking off roaming supprots placing wards, but NEVER shows up when yr pushing for dragon or turret.
the adc needs teamwork. If your team is totally disorganized then really i think there isnt crap your adc can do other than split push, and accept lots of deaths.
many times ive come out of laning phase as adc with a 5/0/2 score or something. and then i see the same pattern over and over and over. its like clockwork. the enemy team will decide to team up...cause they are worried. our yi/fiora/yasua or whatever 'op' champ they are playing wanders randomly in the enemy jungle or something, and the enemy team wins 5v3s over and over and takes objectives. eventually yi tries a desperate backdoor attempt but it fails. enemy team wins. thats your problem right there support...its the guy trying to carry the team without thinking about objectives who is calling your adc a noob for dying 4 times trying to get objectives when the enemy outnumbered him, cause your 'good' player never even showed up.
in fact im thinking of a game right now where i was support leona and the adc was jsut very bad. had no skill. couldnt last hit, and died a couple times in laning phase when they didnt need to. but you know what they DID do? they stayed near me. and 2 other champs did also. Our awesome 'hypercarry' player even rage quit at some point...but because we stayed together as a team and ACTUALLY TOOK OBJECTIVES we totally won the game. they couldnt beat us on a 4 v 5 becuase many of their players were late to the teamfights, and with my cc everything was just easy. it doesnt amtter how good or bad the players are at the end of the day it becomes a team game and about objectives.