I would expect an almost full refund given the time cost, inconvenience, poor experience, stress etc.

Another analogy would be a customer prepaying for a year of fast fibre and the technician telling them that they will be limited to the lowest speed as their provider doesn’t have capacity.

And before anybody says “you could have asked to cancel for a full refund” that is often not a solution even when available - at the last minute alternatives are often prohibitively expensive.

Sure true weather events or natural disasters might be an exception if directly affecting origin or destination but when the cause is the contracting airline not having enough planes, staff etc I believe it is their responsibility to “put things right” and compensate the customer if they have any pride in their reputation.