Does that mean the same number of passengers as 4 DO 328s carried with only 2 F50s?
Yes, BUT the route is one that attracts business travellers, who demand flexibility and timings that match their meetings. With more rotations, there is more choice of flights, so if your meeting finishes early, you can catch the earlier flight back.
The problem, I think, is the timings are terrible. If you need to get to London within business hours, you will need to go to Edi to catch a flight.
It would be easy to totally blame CityJet, but some of the problem lies with LCY. It is so expensive to operate there at peak times that a Dornier, no matter how full is not viable. You need to fill a larger aircraft.
Now you have the problem, that there is a larger aircraft on the route, but because you are not operating at business friendly times, you will struggle to fill it.