I guess you could propose a conspiracy theory that all these people are conspiring to put together fake reports and data sets, but that sounds extremely unrealistic - ad agencies are essentially money-counting businesses like banks, and they take data security very seriously. (Because usually they'd be audited at every step.)
In short, smart people have already thought about these issues, and there isn't any inherent pro-advertising bias in industry, rather the opposite.
The latter is all about incrementality. When you adjust for it, you get the true effectiveness of ads. In some instances, the incrementality will be significant, in others it won't. It looks like that in Uber's case, the incrementality was low. Btw, if you're not familiar with this term, please look it up - there's a ton of literature on it: https://www.adroll.com/blog/marketing-analytics/beginners-gu...
Which brings me to the point about bad employees - marketers who are not adjusting their performance measurement based on incrementality should be fired (and it certainly looks like this was not being done at Uber at that time).
That's a philosophical question of whether you consider statistics to be "proof".
> No one is willing to run the experiments necessary.
You're nuts if you think this is true. I assure you that companies in traditional industries (i.e., without venture capital) can and do run these experiments.
The Uber story is about venture capital and its anti-market incentives, not about the ad industry.