I would say my biggest issue with the travel credit is that you have to select an airline early in the year. I would assume most cardmembers are also leisure travelers and it's just not possible to know in Jan which airlines they are going to fly for the rest of the year. And sometimes I maybe flying an international carrier.

Amex likes to divvy up the credits throughout the year to prevent someone to game the system. So I think a comprise is to reimburse all airline charges up to $25 each for up to 10x a year.