American Express Travel (USA) is currently outsourced to Expedia, but the others are not.
Capital One uses Hopper
Chase uses cxLoyallty (which is owned by Chase)
Citi uses Booking.com
Whoa! I just reread your post. And then I did some searches on the topic of the Chase travel program. So, Chase was partnered with Expedia, for a while. But, acquired cxLoyalty and have been migrating from Expedia still, even in the last year. There was a thread about it on Reddit.
Now it makes sense! Expedia is still lacking, but I believe the frustration I incurred is with the cxLoyalty platform.
https://skift.com/2022/05/28/chase-t...billion-sales/