As someone in marketing. You are right. Many in the field only understand promotion. And that doesn’t make a good marketer. Sometimes it is intentional sliminess, but often it is just a lack of understanding how everything fits together. It is compounded because every client thinks marketing is advertising and advertising is 1:1. It rarely is, but no one wants to hear it. So agencies lie and say it is to get your business, because if they don’t the client will go to the person that tells them biggest lie most convincingly. No one can promise results. It is impossible to say an ad spend of X will lead to sales of Y unless they have already run a similar campaign with your business or product before. Even then it is merely an educated guess.