Check revision ids to determine whether an article is out of date is fundamentally flawed.

With pages that have templates, the revision id does not necessarily change when the page content updates.

This is causing the issue with main pages being stale:
T131377

The main page hasn't been updated since December:
https://en.wikipedia.org/w/index.php?title=Main_Page&action=history

But the content changes every day.

We should determine what other pages may be affected and look into using cache control headers instead.