I can see how you are approaching this but what about this case.
When we booked a daytrip with FR to LBC last May, we found out the day before that our return sector time had been brought forward by about 6 hours too and as a result, we had to cancel the trip altogether as the daytrip would have been about 3 hours long!!
The carrier has not breeched any terms and conditions got you from A to B back to A again. In this case I know Ryanair would not normally offer a refund. Can also understand why passengers would be annoyed. However I know that there is a risk when I book a same day return when I am told that the times are subject to change.
Nothing specifies the time the carrier must keep you at your destination.
I would not expect a refund in this case however there are passengers who would expect a refund.
Warsaw Convention : Article 19 - Delay
The carrier is liable for damage occasioned by delay in the carriage by air of passengers, baggage or cargo. Nevertheless, the carrier shall not be liable for damage occasioned by delay if it proves that it and its servants and agents took all measures that could reasonably be required to avoid the damage or that it was impossible for it or them to take such measures.
Can argue many delays against that , tech, ATC, weather and crew sickness.