Need advice on team fights

So I've been doing very good recently, but I cannot seem to win.

I am a believer that when you have a decently good streak of wins, or good win rate it's set up to pair you with people that are tilted and bad so that you have to carry them. Most people agree that they go from win streaks to lose streaks and so on mostly, versus it being more mixed.

But regardless of that I am trying to see where I might have fault in all of it. Where I might be able to improve to beat the odds of getting shitty teams, and still be able to carry. So I am thinking that one of my weakest points is knowing the balance between peel and backline engaging while in team fights. Its hard to trust your backline to engage properly while you peel for them. I know that while I peel the enemy team's backline will be shredding me, so usually I provide some peel and then once I start getting hit by the backline I engage them. I usually get at least 2 players on me and away from the rest of my team doing this. But, usually it only that's like 1 enemy to 1 shot my backline and soon after everyone else dies and I get left confused as to how my team loses 3v4 or even 2v4.

What should be my thought process? I play Nautilus and Wukong, Top and Support.