@futurebird advertising back in the day was heavy on correlative data to determine success.
Advertising today gives has more direct cause and affect traceability for ROAS (return on ad spend) especially in the form of online advertising, direct marketing, and SEO. Happy to dive deep into this stuff with you if you want.
However to be honest, as far as I know, all this "improvement" hasn't really lead to any sort of decrease in marketing spend as a function of gross revenue.
My soap boxy thing is that a lot of people in marketing departments today want to think they're being very quantitative but in reality they're really bad at it and lack a lot of functional skill. As a result a lot of departments no longer deep dive into customer personas and demographic focused messaging.
Everyone just wants to do scattershot marketing to hit kpis but pretend they're not.