That's a fair point, as that is the primary role of a copywriter. However the author is targeting startups who are unlikely to have the budget to hire an editor

That's a fair point, as that is the primary role of a copywriter. However the author is targeting startups who are unlikely to have the budget to hire an editor to fix the copy provided by the copywriter. It should be part of the package, but on the basis of the OP's own sales copy, it isn't.