I posted before about this but explained it poorly. The new method of having to choose one combination of methods in a drop-down menu of a whole bunch of combinations when creating a listing, is such a total mess I won't even try to describe it. Just two points:
1 - Probably a good idea to check your listings and see if the new system has changed the shipping method(s) on any of them. I just discovered that when eBay changed the method, they changed the shipping on one of my listings - 2-pound package - to First Class Package, free shipping. I wouldn't have even known it, except I was revising the listing to correct another error due to an eBay glitch - (not reducing number available by the number sold) and I got an error message because it had been changed to a method not available. It is going to take me FOREVER to check hundreds of listings to make sure the correct methods are still showing. 
2 - Does anyone know if there is any way we can revert back to the perfectly good, efficient, easy to understand method that we have been using successfully for years?
Have you considered switching to a application such as GarageSale instead of using eBay's online dinosaur listing tools? GarageSale is Macintosh only. If you currently do not use a Macintosh it would be well worth buying a Macintosh just to use GarageSale as it would soon pay for itself and the Macintosh for the time its saves you over having to use eBay's tools.
It allows you to create a series of listing templates based upon shipping scenarios such as services, weights, package sizes. When you have a item that fits one of these scenarios just hit Command + D on your keyboard to duplicate it and then enter you title, description, images, etc... The shipping details are already done.
You can store your templates and completed listings in custom folders along a left sidebar. Here we have a series of templates for Parcel Select items for weights 1 to 10 pounds in the first folder. The second folder has similar templates but offers Parcel Select & Priority Mail, with the last item specifying a 12" x 12" x 12" box.
Here's further detail on a template with a default weight of 20 pounds that offers Parcel Select, regular Priority Mail and a Priority Mail Medium box. The default 20 pound rate is easily changed by clicking on the weight.
You only really need to see the long list of services when you initially setup a your custom templates. After that you simply duplicate your existing template to create a new eBay listing.
You can also use CSS & HTML to customize the description. This a template that displays a simply HTML table for books. The information below automatically appears each time the template is duplicated so it never needs to be retyped. Its easier to ready for buyers as its not bunched up into one large paragraph.
The text inside the {{}} brackets are a placeholder. When the listing is uploaded to eBay by Terms of Service (TOS) will be inserted there.
Here's another HTML table template with borders.
GarageSale allows you to upload listing to more than one eBay account. You can also schedule listings.
