- Anyone else traveling this path for a solution to deleting one-by-one, etc - -
it always pays to "RTFM" such as here:
b/c you learn that a simple check box under "Folder Options" > Save... >
2nd bullet "Save format for all folders (make this the default)" >
CHECKBOX > "Clear any saved folder formats"
will accomplish instantly what took me .5 - 1 hour to figure out!