I've worked with co-ops both on the retail grocery side and ag aggregator side, and the traditional supply chain is similar. The ag co-ops serve as a middleman, and the retail grocery will usually deal with a distributor.
The grocery co-op had way more direct accounts (hundreds) than a traditional grocery, but that was mostly for smaller company specialty goods. The vast majority of the product moving off the shelves was bought from one of two big distributors.
If Lyft and Uber are doing this then I genuinely applaud them. That's astounding ingenuity in screwing over their customers. True innovators.