Perhaps that's true, but if some accident were to happen, UA will get sued along with Sky West, Mesa or whoever was the UX partner. Putting aside the "experts" on FT, the general public thinks that when they book a ticket on UA, they're getting UA expertise in the cockpit and on the ground even if part of journey is on UX. If UA is selling a ticket on an aircraft with UA's name on the side of the plane, UA is vouching for it's reliability. As you point out, they're not getting the same level of experience on UX. But don't point the finger at the passenger for not knowing that, point it at UA management for selling a product that mixes UA mainline and UX interchangably.