Just for an updated reference point. I booked a light fare on LATAM.com They were LATAM (LA) marketed flights, but all DL operated. They booked into a Delta X class (need to check LA fare code). I was able to select my seat assignment on DL (and since it is in an X, the operating carrier baggage should apply). If you use this method for LA marketed/only DL operated you can save a few bucks and get bags. Note I'm a DL medallion, so not sure what baggage allowance shows up for non-elite when you check-in with an LA marketed flight.