I understand that perspective. And I agree that it would be nice if all sites offered the full-text content in the feed. But on the flip-side, I still use RSS feed readers (Feedly) daily and simply click through the content.
The value of the RSS feed reader is still there because it allows you to monitor potentially hundreds or thousands of sites for content and then skim through to see if any new content was created today that interests you.
This makes it particularly useful for monitoring personal blogs or sites that only publish a few times per month or year. I personally LOVE reading people's personal blogs, but since most people only publish a post a few times a month (or less), I am unlikely to check their website every day. I also don't want to give them my email address and have them clutter my inbox with new posts. So the feed reader is nice because I can go once a day and see what new content exists. I skim through the posts and click through on a handful of content that interests me. If the content is long, I add it to my "Pocket" (getpocket.com) to read later.
In the feed reader I usually get a preview of their content (the first few paragraphs). I can read the content and click through if desired. So the feed reader still provides value for monitoring all these sites that have sporadic posting schedules.
I understand the value of reading the content entirely in the feed reader, but I don't mind clicking through the content once I know it is something that interests me. The feed reader allows me to skim, filter, and screen content so that I am only clicking through on interesting content (similar to how HN works, we still have to click through content). If content is interesting, there is value in supporting creators by visiting them on their site to get the experience that they designed and potentially supporting them with an ad or two. If ad use is egregious then I might retaliate by blocking ads for their site or simply removing them from my feeds.