You don’t win the game by being the best at combat but you can certainly lose he game by being bad at combat. (As long as death is considered a loss.
A failed deception or persuasion check may force you into a combat you otherwise could have bypassed but not bypassing a combat only means death if you ultimately die while in combat.
I would say you need to be pretty horrible at combat to really make a difference because 5E is pretty forgiving and even then it's still largely dependent on campaign and DM.
in addition, DPR often completely misses the mark when it comes to evaluating effectiveness which seems to be the OP's point. A wizard focusing on illusion/enchantment/control spells is going to look really bad on a spreadsheet. How do you calculate in the ability of a monk to stun opponents? What's the DPR of Banish?
While I tend to end up with fairly optimized PCs by accident, I don't care how "effective" the other players are. Are they having fun? Are they fun to play with? If yes, then we've won the game.