Having written the above post, I saw that I got a reply in a thread I had posted in. I went to this URL
(via the Subscriptions page), clicked [Reply] on his post, and there the dastardly "Draft" buttons and messages were, under the editor. It performed very sluggishly. I did not click the [Preview] button. The post submitted with no difficulty when I clicked [Submit].
Back on this thread, I clicked the [Reply] button. I now see the "Discard Draft" button on the left. I see "Save Draft?" on the right. Every few seconds it toggles to "Saving..." then "Draft Saved." I wish it wasn't sending what I type near realtime. However, on this thread, even with the draft system now working, it is performing acceptably.