Part of the problem is that AFAIK ED261 requires 75% downgrade compensation regardless of when the downgrade occurs while flight cancellations/schedule changes only incur a financial obligation to the carrier if they're not announced less than two weeks before the originally scheduled departure.

"Cancel" flight flight far in advance: choice to accept rebooking or get full refund

Downgrade far in advance (or close to departure): 75% refund of fare for the segment that was downgraded