Immediately below the comments section, is the discussion area you've previously found. http://discuss.area51.stackexchange.com was added because in proposals, we do want to encourage discussion that is more than just a single thread of comments.
When this change was made, adding new comments was no longer possible. However, it was decided that for some extremely simple, one-off comments, creating a discussion question was too heavy. For that reason, we re-enabled comments, but we still want to encourage actual discussion to take place in the discussion area.
If your comment is something that you are looking to discuss, please create a new discussion for that. Don't try to cram it in to a comment - and if you are finding yourself separating your comment out like you have done, that is a big hint that perhaps it does not belong in the comment section but rather the discussion section. The length limit was lowered specifically to encourage people to use the discussion area for actual discussions.