There is some evidence that big companies (e.g. Ebay) were not wisely spending millions of dollars on Google search ads.

Blake, Nosko & Tadelis, 2015. "Consumer Heterogeneity and Paid Search Effectiveness: A Large‐Scale Field Experiment," Econometrica.

https://econpapers.repec.org/paper/nbrnberwo/20171.htm

I'm sure the landscape has changed since then in terms of there being more accountability (better tools to measure things like ROAI and mgmt demanding stronger evidence of marketing efficacy).