When we talk about "eCommerce" we're specifically talking about websites that simply sell products. Like a basic online store. A lot of these stores spend a lot of effort on the wrong things. In my 9+ years of running eCommerce stores I learned a basic principle: IF the product needs to be explained or has multiple uses, copy is great. IF the product is self explanatory and very visual, images and videos are great. You first need to explain the basics of the product before doing any fancy copywriting.
Here's the small document I'm using in the video: Ecommerce Basics Template.