Eastern did originally use a leased Do328 on LCY, and there were reliability issues. However LCY is pretty niche and Eastern survive on niche, so doubt whether advertising/awareness was the issue.
However NCL-LHR pax dropping? Any evidence for this? There are constant small fluctuations up and down month on month and BA are always tailoring the flight schedule in terms of number of flights and a/c size - the odd rotation being added or removed throughout the year means nothing.