From my understanding, the game is about killing each other lol

Yea, this will always be the problem when trying to create a story around this format of gameplay. You definitely have to ignore the fact that lore enemies can team up because the comp needs it.

The optimistic tone comes across in the character writing, world design, and music. Little in the game is dour or depressing. Instead the focus is on the details that make the locations or characters unique and interesting. There's a lot of language and cultural representation.

Also, barring the secondary deathmatch game made, OW is technically about doing non-kill objectives, it just so happens that killing your opponents is the best way to complete the objectives.

It's funny because on the scoreboard, traditional "Kills" are labelled "Eliminations", but they still keep tradition for multikills i.e. the announcer will say double kill and not something double elim