I am active on a non-Discourse forum where many members will respond to a (sometimes long) post by quoting it in its entirety and then adding one line at the bottom. “I agree” and “+1” are typical responses. It’s not pretty, or easy to navigate.
Clearly better member education would help. Also I suspect that the ease of quoting in replies in a Discourse forum would reduce the tendency to over-quote previous posts.
Still, I would be interested in your views on whether Discourse can - or should - restrict the length of a quote, either through an absolute character limit or via the ratio of quoted to “new” text.