Given how this entire god-forsaken continent wants to do nothing but play Yasuo until the heat death of the universe, and only pick a different assassin because Yasuo is in some way unavailable, no one has any right to say that the game is imbalanced anymore, given that you all do nothing but pick the exact same one single (type of) champion and play the exact one single way.
I have seen it happen so many times, a single microscopic fraction of the true number would make you split open your skull and rip your brains out from the sheer terror. Everyone goes all AD melee assassin or all ADC, and then dooms themselves when they have no frontliners, no tanks, brawlers, mages, crowd control, range, or defensive capabilities, and are constantly retreating and being routed because they can't survive two seconds in front of the enemy team without dying, and can't even get close because a single champion, even a single skill, completely counters and negates the one and only tactic anybody has as an entire team. If that wasn't enough, everyone is constantly going out of their way to screw each other over so their allies die while they get all the kills, only to get killed themselves without taking any of the enemy with them.
If that wasn't enough, people build their assassin with the intention of fighting other assassins and glass cannons. They completely ignore tanks and healers, expecting in the best-case scenario to be able to deal more damage than what Soraka can heal, or that they could just burst through 400+ armor because they really really want to. Nobody builds Grievous Wounds or Armor Penetration (unless it's that fucking Duskblade), so they easily get floored by tanks, their natural enemy, as well as anybody who has even an ounce of healing and isn't 13 levels behind.
And if that wasn't enough, people absolutely refuse to or are completely incapable of defending, which means that the lanes get pushed up to the nexus before the fifteen minute mark. Instead, all-assassin teams just throw that responsibility onto the support, because they don't already have more than way too much shit to do. And people throw a colossal shit fit if the support kills even a single minion, even if it's to defend a lane.
And if THAT wasn't enough, people absolutely refuse to push the lanes because they decided that's ALSO the support's job (only to bitch if the support actually does do it), and basically wait for divine intervention to just randomly blow up the enemy turret, even if the enemy team is all dead and won't respawn for another 30 seconds.
And if THAT wasn't enough, people ignore most of the dragons unless it's an Infernal Dragon (and even then it's a massive toss-up on whether or not they can muster the gumption to take it), even though they spend most of their time running at the enemy only to have their one and only tactic get destroyed by a single slow.
And if THAT wasn't enough, people give up the absolute immediate instant something goes wrong, and they all start mashing the surrender button rather than figure out a different tactic or what they are doing wrong or what the enemy is doing right. They'd rather just bitch about how overpowered or broken the enemy champions are to compensate for their lack of ability or knowledge or foresight or hindsight, even though I've heard that exact same thing said about every fucking champion on the roster more times than there are atoms in the omniverse.
And if THAT wasn't enough, nobody ever learns to not overspecialize and go all assassin. They give up on the game the instant their single tactic doesn't work, only to go onto the next game and expect it to work there, with the exact same overspecialized composition, with the exact same enemy team that can counter their entire team with a single champion or even a single skill. They'd rather focus on the one single thing as a collective and just keep doing it over and over again, lauding the time it works by flapping their mastery dicks and ignoring all the other 99 out of 100 times it doesn't.
And if THAT wasn't enough, this isn't limited to a single division. It's the entire fucking continent that does this, that perpetuates this cycle and refuses to do anything but all be the exact same one-trick pony.
All of this combined has ruined the game balance, and none of it is based on anything Riot has done. This is entirely the community's fault by throwing out most of the elements of the game and expecting nothing bad to come of it. And nobody learns from their mistakes or attempts to ever do anything different. That is also the support's job.