Alright look, here's the roles in the game!
ADC-Attack Damage Carrier otherwise known as a marksman like Miss Fortune, Graves, even Kindred, they build attack damage and ditch out damage over time through their auto attacks relying little on their actual abilities reserve for special circumstances.
Upside-Sustainable damage, this is your damage dealer, in team fights this is the fucker that's doing most of your damage usually. So last thing you want is your adc to die.......so your team needs to make sure the heavy assassins that are playing in bronze can't get to your fucking ashe, the more you protect your adc, your chances of winning increase.
APC-Ability Power Carry otherwise known as a mage, not a support, but an apc that's building ability power, Ziggs, Xerath great examples. They rely solely on their abilities usually throwing down abilities into combos, they force the enemy team to build MR so that late game your adc can do damage without being resisted, this is especially true to those pesky players that love playing Assassins mid, some exceptions like Katarina and Kassadin are different because they are also mages.
Tank-Okay this one is obvious soak damage and usually in the front lines, should be anyways.......If you are Nasus, Garen, even Darius, a lot of people don't know this but they can tank, they aren't just bruisers.....Build defensively and hold the line, keep assassins off your carries, and take the damage, you should be the first one in, and the last one to leave the fight.......Okay.......okay so why are you chasing through the enemy jungle after Master Yi, how about instead you stay in front and trust that your team will win this team fight, if you are to die, so be it, at least all the damage is being done to you and not the rest of your team.
Bruiser/Off-Tank- You are not an assassin your job is to disrupt any frontline they may have. Get through get to the carry if you can if not fine disrupt the front line spread them up, make it easier for your team to prioritize targets. Vi, Xin Zhao are great examples of brusers, don't go chasing down the adc, stay in the fight beat up some people and push the adc away from their team, so that your assassins can take care them easier.
Assassins-Your not the carries, you will not be doing the most damage, you might have the most kills but you aren't the damage dealer, your job, see that Ashe, and that Morgana, your job get to them, kill them, chase them until you kill them or you die, keep them away from the team fight, be smart don't go in knowing your going to die. Assassinate your target get out of there, come back after your abilities are off cooldown and take out another target.
Support-You are the team's mom, or dad whatever........your main goal is to watch over your team be that wall like Braum, initiate the fight like Leona, pop that game changing ult like Soraka, aoe their entire team like Sona.......keep assassins off your carries, that is your main goal, it's not the early game anymore.....so what your job doesn't change, why are you Morgana running after Jinx? Stay here and ult their fucking team spread them apart shit.
Their is your roles on a fucking pedestal!
And then their is the infamous hyper carries, Master Yi, Yasuo, okay these champions most of them were design before the current meta came into existence, every since that meta, Master Yi, and several hypercarries aren't viable later in the game stages, say gold and above with well coordination not seen in low level play Master Yi as well as a lot of these type of champions don't do so well. I like to consider them as cheese champions kind of like a 6-pool for Zerg against Terran, it works sometimes, it might even be able to get you out of bronze but once you get to silver maybe gold, and that's a big if........you'll be shot right back at the bottom because instead of mastering more team oriented type champions, you chose to master Master Yi useless pass bronze and silver. Reason being unless fed, they serve no purpose in the game.....like a 6 pool if it fails the game is as good as over, same with these type of champions. Yasuo is one the few champions that can hyper carry a team in bronze and is still useful in all stages of the game, he no longer would be considered a hyper carry in gold and above and becomes a strong assassin/Bruiser depending on how he builds.