when a 70% winrate player is inting in your game and tells you that you suck with 48%winrate.

im hardstack in diamond 4 as you can see from the winrate but why? why i am still diamond 4 after a lot of games who are close to 400 and still cant be more than diamond 4 tell me please did i suck or my team is always iron tier?because everytime i play a game my team is dying solo or not helping me when enemys push the lane so how can i be good to the game? i buy a lot if vision or trying to help my team still cant do nothing is that enough to realize how i feel?