F50 is fine... yes and no. The early morning flights from ANR to LCY and the evening flights from LCY to ANR are almost every day fully booked (even one week in advance). So last minute business passengers are no longer able to book these flights. And since last year demand from Antwerp Airport is growing again due to the expansion of the airport.
I think Cityjet should change to a RJ85 on the ANR route too. Two daily RJ85 morning and evening service Mon to Fri + once Sun would mean 1045 weekly seats (one way). Now with the F50 they offer 900 weekly seats (one way). So not a big change.
In between they can offer direct flights from ANR to Cork, Dublin, Avignon, Toulon...