Yeah, GHD has not been well-marketed, but I've used it a couple of times and it has been very useful. I have similar experiences where SO questions can be pretty dodgy based on age--for example, for Rust I rarely bother looking at answers from 2016 because so much has changed since then. Some technologies are more stable than others.
Usually a highly voted answer that is no longer correct will be updated through time. I don't have any data to support this claim but it's what I see happening.
Probably, but that furthers my point: that "update" is new content. The original content is not especially valuable; the new content--the user activity--is where the value is.
