Agree, but I'm speaking more in aggregate. And even individually, it's not hard to find people who will say that e.g. an Instagram ad gave them a noticable benefit (I've experienced it myself) as you can who will feel that it was a waste of money.

There's a tiny slice of companies deal with advertising like this. Say, Coke vs Pepsi, where everyone already knows both brands and they push a highly similar product.

A lot of advertising is telling people about some product or service they didn't even know existed though. There may not even be a competitor to blame for an advertising arms race.

A monetary economy can't function without advertising or money.

You're tilting at windmills here, we can't go back to barter.