senior editors and baseline quality

There would still need to be some sort of approval process, managed by bureaucrats. And part of that approval process would be showing that you've been a major contributor to however many FAs. Maybe by having someone who worked on the article nominate you, or maybe by providing some "diffs".

And then there would be a recall process for anyone who was deceitful, and became a senior editor by lying about their contributions to a FA.

All that would make it very unlikely that someone could game the FA standard.