Here's another example (different airline, I know - apologies!):

I book an AMS-LHR-SYD-LHR-AMS Business Class trip on British Airways. I am downgraded on one sector (AMS-LHR).

Who would seriously argue that it would be reasonable for me to expect the airline to refund 75% of the ticket price (less taxes and PSCs)?

(I do however think that a higher rate of compensation should be paid if airlines deliberately downgrade passengers in order to use aircraft with fewer cabins and with the intention of selling seats in these cabins and/or accommodating overbooked passengers in these cabins. This is quite different from downgrades which result from circumstances deemed to be reasonably beyond airlines' control.)