Instead of complaining why don't you re watch your games and see what is going on? Check your op.gg when I lose to much I don't blame my team I blame me. I can carry games 1v5 with kog, cait, and ez. I know this so why play another champ I am not too comfy with? You don't if you want to climb. Pick 3 champs master them. Stay positive. Support your teammates. I have supports that wonder off to ward multiple times and die when they could have waited 5 more seconds for our jungle but instead ill normally say " no worries homie" or " you doing good we got this" even though its clear we don't, but I am a leader in real life and I take it in the game. Though I just started league not long ago 4 months? or 5 months? I see this is a common thing in this game where people go on big losing streak and don't know why.
Watch youtube videos on guides on how to play darius or gragus.
Watch lcs matches that have those champs in them ( gragus is played a lot )
Find streamers that are playing him
use practice tool. <--- riots god gift to us all
what are your keybindings?
do you play locked camera? Do you use both?
What is your cs 5/10/15/20 mins on average?
Do you know all the champs in the game and what they do at each lvl?
Do you know your champions power spike?
Do you know your champions item spike?
There is so much to this game its crazy but if you want to improve that is just a small list bro.
Any questions just ask. Though I am only silver 3 I am climbing fast and have a good understanding of this game.