Why do they always flame and brag like they are league gods at the end of games? If you have 10 kills, but only 15k damage, and every other damage carry on the team is at 30k damage, do you really think your kills mean anything?
Actually kills (and assists, and low number of death) can mean a LOT more than damages dealt.
I can play Nasus vs Mundo toplane and we will end the game with more than 100k damages dealt while none of us killed the other nor did anything revelant. Just because we regenerated all our poke again and again. These are impressive numbers, but useless ones as well.
If you let a botlane Zyra+Caitlyn vs Vayne+Brand play they'll have really low damages per kill because they'll basically all in each other everytime, making : damages dealt / (HP max * number of death) close to 1.
Now take a botlane : soraka + Varus vs Nami + Ezreal, they can very well poke each other without dying EVER just back a bit under tower, heal, come back farming, poking around. their damages dealt / (HP max * number of death) can be very high, but these were not usefull damages at all.
If you are always present at the good place to get the last hit, (assuming if you were not there, there couldnt have been a last hit from another teammate), you are as usefull as the one who did the "big part", because all his work would have been useless if you werent there to transform it in an actual kill.
Another nice addition i tough of :
Let's say you are the only AD in your team, it means the ennemy team will stack MR, so you will be likely to deal WAY more damages than your mates, but it doesnt mean you are playing better or anything, it's thanks to your team composition that you are able to do that.