My question was initially intended for products, and I am using “Product Vendors” from Woothemes to prevent vendors from editing each others products. I still would like to use the Page Builder for my own / the stores products. I would then need a way to let the Admin user have access to Page builder on products, and refuse other users the same access.
I have not tried the editor role in the blog, so I did not know every editor could edit all posts (which sounds strange, it would then not be possible to make a blog network) – but I will still ask if it is possible for products.