Advertising is at its core a prisoner's dilemma. If every competitor in a certain space puts in $100 in advertising, they can all expect $0 in returns. However if a single company put in nothing they would be in a worse place because their competitors' returns would automatically become higher.
You mean zero-sum. Advertising is a zero sum game. I can't find the tweet but someone referenced the fact that if you lump traditional and digital media together, the TAM of advertising has basically been stagnate for decades. We just think its grown because FB/Google/etc have gobbled it all up.
It is definitely true that the economic benefits don't accrue to the advertiser! And it's also true that the economic benefits decrease as advertising saturates. But it's still not zero.