AL were losing money in SNN during the winter and hence the reason why the A330s were pulled out and reinstated for the summer. No charity there.
What SNN is getting now is the opportunity of a year round service to JFK and BOS, initially on a 757 and then the NEOs when they enter into service.
Of course as everyone should appreciate aviation is a cyclical business and is impacted by many external forces. At this present time the 757 and NEO is a good fit for somewhere like SNN and it has the added benefit of freeing up the A330s to fly further afield. Who is to say that in the future that the US dollar doesn't strengthen against the EURO and that there is an influx of US tourists spending it up large. In which case the business case is then turned on its head and bigger hardware would be required.