I'm an e-commerce manager. Let me start with the numbers, I'll comment later.
We have thousands of products in our catalog. Some are live with the description from the manufacturer, some with descriptions we wrote ourselves. Same category, similar price range.
Products with our own descriptions have significantly higher search traffic and add-to-cart rates. The difference isn't small, it's multiples.
The reason is simple: the manufacturer's text is the same on hundreds of sites. It's impossible to rank with that text because a hundred other sites are using the exact same sentence.
So what should you write? The structure that works for us is: what the product does in the first two sentences, technical specs in a table, who it's suitable for and who it's not suitable for in separate sections, and FAQs.
I want to emphasize the last point: the "who it's not suitable for" section lowered our return rate. We thought it would reduce sales, but it didn't.