I'm just trying to say to you - yes I also have direct experience with this, so don't try and give me some anecdotes. We ran meta-analyses across hundreds of clients / experiments using advertising, both retargeting customers who abandoned their baskets, and consulted on more traditional experiments as an independent auditor. These were mostly in the fashion and travel verticals. The revenue uplifts we saw as a whole across the sectors were poor, expecially compared to other things that these sites were doing (social proof, scarcity etc.) I never once saw a value like 6x ROI. We could not publish this publicly unfortunately, as it more generally showed that stuff people were A/B testing doesn't really do much, which would have been bad for business.

This does not mean that search advertising is useless as a concept. But the idea that it 'just works' is also clearly false.