For example, one of the articles linked to earlier quoted from one of the flight attendants saying that it was a pax who tried to open the rear doors, despite the FA being there. So yes, I would say at that point the cabin crew role became very relevant!
I'm sensing it's difficult to make the point that CC effort was of little importance in this particular incident, without it being interpreted as a broad attack on CC in general. There are incidents where the CC's actions made a huge difference, but this (fortunately) is not one of them. Of course, the picture is far from complete, but the reported actions performed by the CC didn't appear to have mattered much. 1) Brace position reminder called on PA, excellent thinking and action taken, but landing was soft enough to render it irrelevant, maybe risking a couple sore necks at worst. 2) Life vests information, some concern on pax lacking them, but it didn't matter as the ferries were able to scoop up the people in time. Questionable situational awareness on the CC if they did not know they were landing on water until the aircraft had started sinking. 3) Opening of aft doors, this is infact a point I believe very few pax would be aware of. Yet several reports of people trying to open them, halted only by the fact that they did not open, not CC it appears. Reports of water leaking in might be due to the doors being opened (to some degree), but again they all had enough time to get off safely anyway. Opening the over-wing and front doors and wait for the ferries to come, I believe the passengers would have managed that on their own. Again, they are in an aircraft that is sinking on the Hudson. Try to stop them getting out!
Replay the flight without any CC or incapacitated CC, and the outcome should be pretty much the same. That's the definition of irrelevance, isn't it? It's similar to if your house catches fire, and you manage to put it out yourself before the fire trucks arrive. The fire brigade would be completely irrelevant for this particular event, that doesn't change the fact that in other circumstances they can be the difference between life and death.
Of course, there were passengers floating around in rafts, which would have to be filled with the right amount of people and then detached. Perhaps without proper use of the rafts, people would have to swim, and there would probably be some fatalities. However, I would guess that the passengers would be able to organize this rather simple task on their own, especially with the flight crew available to give orders. So I'm stumped in trying to find areas where the CC would have made a difference this event, in different circumstances, sure, but this incident? Hence I claim they were irrelevant to the fortunate outcome. I would be happy to change my mind from new information.