People really need to learn about the difference between roles and the words assigned to it.
Supports do not only heal, Tanks do not only soak/prevent damage, DPS do not only do damage, they provide utility and versatility to get kills that others dont have.
Tanks are Enablers and Openers (can also finish targets sometimes)
Healers are Enablers and sometimes Finishers
DPS are mostly Finishers and sometimes Enablers (can also be Openers sometimes)
They are the best finishers by far because their one shot combos/potential and their damage is not “capped” just like the tanks.
It doesnt matter how awesome you slap people with rein, you will only do 75. But if you are Genji and nail your triple +swift + melee you can finish off A LOT of targets that are a bit damaged on health, in a row, like in 3 sec.