Ideally, you could support this informed opinion with some studies? Preferably not just general anti-ads clickbait.
Sure, you can’t ever /really/ know if your “inception” in the case of branding campaigns worked, but product/seasonal campaigns are super easy to measure and prove.
And so, "to the best of my knowledge, this is unsolved" is not an opinion but a fact.
I am happy to be proven wrong with the relevant material.
And by material, I mean scientific papers, not assertions such as "product/seasonal campaigns are super easy to measure and prove."
And so, if you google-scholar (not google) for "online advertising incrementality", you are left with (granted, excellent) work that shows that nothing has been proven yet and that it is a very hard problem [1].
And when customers of Google, Facebook and other ad tech companies ask them about incrementality, their answer is surprisingly quiet.
[1] https://dl.acm.org/doi/abs/10.1145/3447548.3470819
PS: I don't make any hyped claim that ads don't work. I question this fact in a constructive way.
Proving specific incrementality is rarely a concern from actual customers, unless they wanted to tighten their purse strings. Nobody questioned if actual incremental gains could be made - only whether there are diminishing returns for their increased spend.
My understanding of the field is quite the opposite. The only way to measure the true value of online advertising is to measure how much sales have been generated with ads enabled minus the sales that would have been generated without the ads.
To the best of my knowledge, this is unsolved, even by the giants who have plenty of talent and data to throw at the problem. And for a reason, this is a very hard causal problem to solve, with many (many) confounding variables.