Nobody that says this ever says what champion they play or the rank they're at. Literally just pushing that hate train along and people eat it up.
If people actually told others what champion they play when they say that line, it'd be significantly easier to shut them down.
Right because there's absolutely no champs that cant be shut down by certain matchups due to weaknesses in their kit. 
(weird that most of these have had their counterplay elements removed, or have been buffed so much that their weaknesses don't matter.)
There's also no such thing as champs that have massive hitbox issues or game breaking bugs that lead to them winning or losing their lanes, regardless of skill.
and there's totally no champs that are purposely strong and not nerfed because they make tons of money on selling skins for the champ, or have balance bias because favorite waifu. 
There's no such thing as champs that are buffed or changed to become relivent in pro play or high elo, while their kits are stat check and pure cancer to deal with, leading to over buffed nonsense. 
And last but not least, there's NO SUCH THING as champs left to rot because they don't sell said skins, and they are too lazy to update them, another champ does their job better, or they just aren't flashy enough to be in pro play/be in the meta 
I seriously cant believe that you are this ignorant to just ignore ALL of this, (and this doesn't even cover the items or general game balance/bugfixes) and claim that "People are just pushing that hate train and people eat it up". Either you haven't played in awhile and haven't kept track of whats balanced or not, or you are extremely ignorant and are on the shortbus of people that think "Riot can LITERALLY DO NO WRONG AND THEY ARE COMPETENT DESIGNERS, THE REST OF YOU ARE JUST TRASH".
200+ years of game development experience indeed
[zombie-brand-facepalm]
Because if someone mentions the champ they play and what rank they are, it's like automatically they have no right to say an opinion or anything.
This goes beyond what champ you play and what rank you are. What's critical is how constructive you have about a champion. From discussing what their kit does, how it feels to play with, as and against, making sure you understand the champion at least the very minimum, win/pick/ban rate, and perhaps even change suggestions.
If people actually told others what champion they play when they say that line, it'd be significantly easier to shut them down.
This is just piss poor. So if someone says something about a class or champion, even if it's 100% valid, fact, concrete, and true, it becomes ignored simply because the dude plays a champion that happens to be problematic? When someone opens a topic about a specific topic, you stick to the topic. Going on someone's rank or what champ they play is just going off topic and can lead to a different and even heated discussion.
It's simple. You read what people say, see if they are valid, see if it makes sense, and you reply.
Because they don't want to be called out. More often then not, they are complaining about a role and/or champion they don't play, whine it is OP, while maining a champion that has like a 52% win rate or some stupidity like that.
The vast majority of people who play this game don't want balance anyway, they want fun and personal enjoyment and constantly confuse it for balance.
Tyler1 has said it, so...
Enchanter main.
Dominion - Unranked and Dominate Dominion Tournaments. Twisted Treeline - Unranked. ARAM - Unranked.
Come at me. ;p
I think a big part of it is that the vast majority of balance QQ should really be feel QQ. A good example of this is Lee Sin. All over this forum you will find people whining and whining nonstop about how OP Lee Sin. And to their credit, Lee Sin is universally loved and hated, with both the highest pick rate and the highest ban rate among junglers. However, the reality is that he's just popular. He gets to do flashy stuff, and so people want to play him. He actually has terrible win rates in all MMR brackets until you get to Master, at which point he finally breaks 50%. Until then, having a Lee Sin on your team actually makes you LESS likely to win a game. And even, in Masters he's still outclassed by numerous champions, including Pantheon who's rocking a 55% win rate, Warwick who's at 55%, Master Yi who's at 54% (wtf I did not know this, probably the funnel). Should Riot nerf Lee Sin to "balance" him for .1% of the player population?
Nobody that says this ever says what champion they play or the rank they're at. Literally just pushing that hate train along and people eat it up.
Im unranked and a Yuumi main.
While i dont think riot simply doesnt balance... Riot does do limelight balancing and knee-jerk, which is where they purposefully create problems to shift metas while protecting their favorites and over-reacting to niche strats/sudden popularity with nerf bats. Those -5MS, -2 base AD nerfs we meme about? Those are what happens when riot puts a favorite in the limelight.
Those random ass buffs we saw the last two PBE cycles - including the wukong changes - are from limelight balancing, too. They want a flashy wukong who can make plays so he becomes popular... But he has fans within riot, so he cant be TO flashy or play making otherwise hes going to get heavily nerfed. From what we know of riots internal culture, theres very little chance that the game actually has a direction or that overall balance is an actual goal; Its probably very likely that riot wants to balance the game for their favorites and the last twenty champions released without worrying about older champions (and occasionally modernizing older ones that have fans internally).
