Re: Previous approach
When I was at Google, we had a presentation from the analytics team. The presenter mentioned that the team and proposed to create a metric so that advertisers could track the effectiveness of their ads.
They were told "no" in no uncertain terms.
Google obsesses over measuring everything. They had the experimental results of targeted advertising in days, and full information in a month. It is bad for advertisers. They have know it for so long that the implementation team lost the institutional knowledge of that fact. That was already true six years ago.