A very easy way to break this argument is to not look at huge known companies like eBay and Amazon, but brand new companies 1-2 years old that have grown almost entirely by online ads. Eventually word of mouth kicks in, but there are plenty of smart operators that built their entire brand and revenue off of ads. Works best in online direct to consumer brands.
Reliably someone comes along every few months to question digital ads. I always come back to analyses of incrementality as the real proof. Take an audience of X people. Divide them in two. Show ads to your test group, don't show to control. Watch your business grow and gauge the lift between the two audiences. The companies that know how to advertise at scale do this constantly and can gauge the real effect of their…
It is something that could work for retargeting existing users but doesn't work for acquiring new visitors.