It is Ryanair shareholders who suffer this market punishment, they have the power to dismiss Ryanair management. Where Public servants mess up their customers have no such power to dismiss them. Voters have the much less power to not reelect the political masters of public servants, at the next election, when every other aspect of governing the country has to be considered as well.
I don't disagree in general with your points but I suppose the point I am trying to make, which is my bad for not making it clear, is that there is a tendency to admonish the public sector and all its apparent failings while pointing to the lack of accountability. This is followed with the somewhat exaggerated claims that if such failings occurred in the private sector then the axe would fall on those responsible, no questions asked. This is proffered as an effective way to foster maximum productivity and efficiency, hence its good value for consumers.
The reality is far from this. When it comes to accountability in the private sector, most managers will automatically will adopt a strategy of self-preservation pointing to system failures rather than personal accountability similar to public sector workers.
This is not a criticism, this is just an acknowledgement of the reality of working in large organizations. That when the worst hits the fan, both public and private sector worker's will react in similar vein.
In this case, the CEO is accepting responsibility, not for the cock-up in scheduling, as he is unlikely to be directly involved, but for the subsequent fall in share prices. And as you have pointed out, the shareholders can get rid of the management if need be.
Ditto public sector, when the worst hits the fan the buck will stop at the Minister or Commissioner or whoever. But the worker's in the public service are then lambasted for the 'protective culture' etc, when in reality, private sector worker's, working in large organizations, adopt the same methods of self-preservation.