At the far right of the column headers is a little icon (see attached image). Go to a folder that you have set the way you want, then click that little icon.

At the bottom of the pop-up menu, is "Apply columns to...", point at that, then, "Folder and its children", then the account you want, then click on the account name in the final pop-up menu.

Thanks for pointing out that tiny icon, Bruce, I hadn't noticed it before!

Unfortunately, your suggestion didn't work for me as "Folder and its children" only seems to apply changes relating to the addition and removal of columns themselves - not to the sort order within those columns, which, for the Date column, still sorts into chronological order (latest first) for both new and existing folders and sub-folders.

Edit: I've just noticed that I made a mistake in my original post - I wrote "with the most recent message at the top" but I meant to write "with the most recent message at the bottom".