> But I've heard that it requires creating a massive feed file containing many articles, including text and images
So a) no, it doesn't contain images, just URLs to images where necessary; an RSS or ATOM feed is just a text XML document adhering to a certain schema, and b) the feed file is only as big as the site decides it needs to be.
For example, a typical blog or news organization could generate a feed containing the last 24 hours worth of new content. Feed readers will poll that and pull in new content while ignoring existing content.
In short: this should be a non-issue unless you're turning out massive amounts of new material on a regular basis, in which case you're probably a major news organization and can afford it.
> As a result, some blogs (like christine.website) stopped serving article contents in the RSS feeds.
This isn't because of bandwidth concerns. This is because they can't advertise in an RSS feed so they want to drive eyeballs to the site.
Personally, I run ttrss and use a plugin that scrapes the content from the source site and embeds it right in my feed. As a result I only have to leave my feed reader if I really want to for some reason (e.g. to read comments on the originating site... like, say, HN!)