HunkyBill is absolutely right. You'd be surprised how low tech these shipping warehouses can be. Then again you might not. Remember the use case here are the many fulfillment houses designed to move hundreds if not thousands of different product lines for different merchants each day. I've seen some of these places have up to 100 lines to pick pack and ship boxes all day.
You are right. The mapping in Shopify is not the best. Plus every warehouse I've worked with has different table formats anyways. That's why csv is easiest cuz it's universal. We do let you order and configure the table fields as you chose so it's usable by your chosen shipper. It's not a perfect solution. But we tried to keep it simple so it at least takes some of the hassle out of using anyone other than Ship wire.
So far we've gotten it to work with 2 clients using 2 different warehouses. Would love to get more users before we declare that "it works"