'Damage dealt to champions' is often a misleading statistic because a champion's damage isn't dealt in a vacuum. It tells you nothing about the damage you dealt to specific key champions at key moments of battle. In other words WHEN and HOW you deal that damage is what is extremely important.
For example: our Varus was poking like a monster throughout this ARAM game (highly favored for poking champions) and doing relatively well in a few of our skirmishes (only approx. 3 huge teamfights in this game). He was definitely our main damage source and we relied on him to deal that damage while we peeled and disrupted the enemy team. But he took 4 shockblasts to the face from the enemy jayce before the last teamfight started and got taken out immediately because he had like 200 health remaining. Yes, he did much more damage than anyone else on our team but he single-handedly lost us that game because he could not position or dodge those last few critical Q's and left us to get run down in a 4v5 with no real damage source.
He dealt the most damage throughout the game because of his poke but when it really came down to it he failed in the most important teamfight and did no damage during the time his damage was needed most. He lost us that game. The 'damage dealt to champions' stat is misleading in that game because his damage was dealt periodically over a long game; not in our game-deciding teamfights.