You missed part of it.
You create the Album Artist (Sort) field that 6233638 suggested. You set your view to
Sort on it (via a rule added to the Files to Show search for the view), but you do not use it to
display information. In other words, you sort on it, but you don't need to see this field in your view anywhere, in the view, you just display the "real" Album Artist (Auto) field. Sorting does not
have to be connected to the columns that are visible in the view.
Also, I think you might have messed up the expression a bit (or 6233638 did when writing it). It should output
only A, B, C, and D. I'd actually use 1, 2, 3, and 4 instead to avoid the Article ignoring issue. So, it would kind of break them up into four rough "categories", where you can sort these categories in the order you prefer.
When creating your Sort order in the Files to Show search for the view, you first sort on this field, and then sort on your real [Artist Album (Auto)] field.
You may also want to look at
my [Artist Letters] custom field example. I use this for writing folders to disk, and you can use it as a sorting or display field too.