[naravara]

>Over the same time, the industry has gotten much more sophistication in measuring return on ad spend. All while growing by leaps and bounds.

The trick is, the ad industry people are the ones who design all the KPIs that determine the efficacy of ad campaigns. So there's a bit of a self-serving incentive there that could be degrading the quality of the information.

There is clearly some evidence that ad spending does help, particularly with building brand awareness and goosing demand. I think the jury is still out on how much and to what extent specific user tracking/targeting strategies work though.