> advertising isn't nearly as effective as advertisers let on

Most marketers should know exactly how effective their ads are by measuring to the end of the funnel. This is standard for most business and while bots are a problem, if you're judging online advertising at the front end of the funnel that's to a large part on them for a bad setup and/or optimisation.

Let the Google Ads account run dry, discover your Analytics never actually goes down. It was just donating to multibillionaires the whole time.