Who said anything about existential dread? Perhaps the fact that dread is your reaction speaks more to your relationship with mortality than to the site’s approach.
Fair enough. I guess I read your statement as universalizing that feeling. That is, when you said "this type of messaging ... does nothing for you except make your mental health worse" it didn't seem like a statement about your reaction; it seemed like a criticism of the site.
It probably isn't just you, but on the other hand, if we were to agree that existential dread is a less desirable reaction than some others (and it might not be!) there doesn't seem to me to be an obvious way to develop those more desirable reactions through methods other than exposure therapy via these sorts of sites.