Actually UA probably benefits more from credits via Amex. Most Chase UA cardholders have a UA card because they actually fly UA. But when an Amex cardholder gets a UA TB credit, he or she is forced to fly UA at least once to use it up. So this makes me wonder if this was somehow unintentional on the part of UA and we'll see a change rolled out to address it. Cutting off the GC route on DL makes sense though, but that's because Amex and DL are partners and DL wants to keep Amex happy.