All sane blogs should have <link rel=alternate ...> meta. It seems like you are trying to use heuristics to guess beyond that; while I appreciate the usefulness but I think it may encourage sloppy code and inequity between large and small platforms.
I agree with you but unfortunately that isn't the reality that we live in. It is nice to have a tool that can know about popular websites and help people start using RSS even if sites aren't "fully cooperative" at this moment.
Also some sites don't support RSS but there are public services available that can help out. (Ex: nitter.net for Twitter.) I was talking to the author earlier and they were considering adding a "third-party" section to the response. This would allow getting feeds even for sites that don't support RSS natively.
Also as awesome as an alternate link is, the reality is that most browsers don't do anything about it these days. Even worse, the most popular browser (mobile Chrome) doesn't even support extensions that would allow adding support. So it is nice to have a nice accessible frontend for discovery. The extra heuristics are really just a bonus. (Of course if all feed readers supported discovery this wouldn't be as much of an issue but the reality is that the most popular readers don't. So lots of gaps that this tool fills)
I really need to get around to writing the article I want about how to set up a feed for your website with all of the best practices. Some day...
