Overspecializing - And still you don't get it.
Do you know what happens when everyone goes all AD all melee all in all damage all glass cannon? You get countered by a SINGLE CHAMPION very easily, and if the enemy sees this (and they ALWAYS DO), you are FUCKED!
If you depend on one champion (read: the support) to do literally everything that isn't damage, you are FUCKED! The enemy will just focus them to rob you of that one advantage.
And literally nobody I have ever met in this goddamn game has even begun to understand this, and they likely won't, even given fifteen quintillion lifetimes to learn. Most champions out there are NOT overpowered; most of you out there have overnerfed your amoebic brains and play into the strengths of 99% of all the champions. You accustom yourself too much to playing against players with the competence of a coat rack, so when you actually face against a REAL menace, you shit yourselves and scurry to this forum to complain about how everyone is overpowered. And it's not just one single person that does it; literally tens of millions of you have the exact same mindset. You only pay attention to arbitrary numbers and statistics, you don't actually pay attention to the game itself, you don't adapt to anything, and you don't alter your playstyle outside of an all or nothing 1v9 mentality. THAT is why you are stuck in an "elo hell", and once you break out of that mentality, you'll actually get better at the fucking game!