I think we agree - it doesn't matter if the airline tells you in advance if there has been an equipment swap. If you turn up on the day of your flight and you have to sit in a cabin lower than the one purchase involuntarily, compensation is due.

This is unlike if you are denied boarding due to cancellation, in which case there is a reasonable notice period for an airline to tell you in advance: 14 days at least.

If EK want to avoid a compensation claim then they should refund the entire ticket - I agree the absolute minimum should be the legal entitlement of 75%, whether that's on a per sector or trip basis (whenever that gets resolved at the ECJ)