There are several ways the damage graphs may be inflated, even if the damage you dealt didn't actually result in kills or progress for your team.
* If you're Brand or any similar mage with Liandry's and Rylai's against a team with tanks, the fact your abilities are AoE and deal %HP damage will inflate the graph because it uses the flat numbers.
* If you're Illaoi or a similar short-range champ and run into the entire enemy team alone, deal half of everyone's HP, but die without a kill, the damage graphs don't reflect them getting away and/or healing it back up.
* Likewise for when you don't have Grievous Wounds but keep attacking the ones getting healed instead of the healer.
There are other and more specific examples, but that's just a few. If your damage didn't result in gold for the team, it's meaningless. And even if you want to act like it matters for a loss, you should be looking at your damage compared to the average for your champ for a game of that length, not compared to your teammates.
Nor does it matter if you dealt more damage than an enemy with twice your kills and assists and half your deaths, when you lose anyway. It's _especially_ ridiculous to mention damage graphs in that scenario.