If website you visits asks you to confirm that you are a human user from some 3rd party API isn't that same as requiring captcha?
You can still have browser extensions that filter the ads away after the website sends you the final HTML, right?
Not if there's only one browser that you're allowed to use, and it's owned by the world's largest advertising company.
Also what would be the benefit for other companies to agree to have their customers be vetted by Google run API that excludes portion of customers?