The intent is clear, yes. But given how well-known this problem is by now, I would expect a company of the size of Google to have a practical solution to combat

The intent is clear, yes. But given how well-known this problem is by now, I would expect a company of the size of Google to have a practical solution to combat this sort of scam, e.g. requiring that the vanity URL points to page containing a specific advertiser ID in the HTML source, or that the canonical URL of the URL with tracking parameters points to the vanity URL, etc... There's so many solutions to this problem that allow vanity URLs to continue to work. Google just doesn't care.