Rengar carry

So i have been playing alot of rengar past couple days and I have been going off with him. Many games going like 22/8/15 12/4/5 and losing these games. Those are just a couple of a long list of games i have done very well and still lost feel free to check my lolking or match history. Especially early game i dominate the enemy get myself around 10 kills with only a couple deaths at most. I know i cant win every game such as a recent one where i went 4/2 and my team lost 4/17. But im able to stall the game to late game where every one is full build and i can normally take out their adc and their other carry often the midlaner instantly. Yet while i do that my entire team has already died and leaving me to take the rest of them on. Im currently gold 5 climbed up to gold 1 promos to plat about a week before the season ended and cant seem to get out of even just gold 5 now. No matter how good i do i cant seem to win all these games when im getting super fed and snowballing my entire team. I have tried giving ALL kills to lanes and they still get destroyed. I know people say elo hell isn't a thing but I starting to believe in it. Also I would prefer not just having the basic tips I can find anywhere such as "just keep snowballing ur lanes" or get objectives. I have been getting the first 3 dragons for my team almost every game as well and i help push lanes all the time to get an early tower so they can roam. I have been getting really good at telling my team where the enemy jungler is counter ganking them and keeping a positive attitude always using my advantage yet my team is arguably useless every single game. Even when i do win, its a close game and i have to get a quadra at the end or do all the damage to everyone on the enemy team. I've been making really good baron calls, good map awareness, helpful pings, ect. I really have no idea what else to do! I have a friend who is plat 2 and I duo with him sometimes and do just as good and he says he has no clue why im in gold 5. If theres any really specific tips anyone has that would be great because idk what else to do at this point.