Sorry I did not read all posts but it seems feasible to bulk delete all products (but ecommerce synced) in the product screen.
select the first 20
System will ask if you wish to select all product (or the result of your search
it will remove the top optiosn Move or Delete
you clik on the option on one product ligne
it will allow you to delete
the next screen will ask you to confimr how many showing you already the number of product select
confirm the number and validate
and it is done (could take some tim depending on the size of your catalog)