Hi. Discourse is a discussion platform (forum), while Disqus and Cusdis are comment widget that embed to existed website (like embed in blogs). I think they are not the same.
Discourse is heavier as a forum, certainly, but it supports embedding in sites as a comment section, and will generally do useful things like "automatically create a new topic of discussion from the post."
I agree that it's exceedingly heavy for comment only use (and generally requires user accounts), but if you're trying to build a community that also has blog posts, the two do integrate very nicely.
