Its more the prop perception rather than the Q400 aircraft itself.
DUB did not work for BA against WX
BHD did not work for WX
EDI was loss making for WX against BA.
With the exception of Switzerland, can any LCY route profitably sustain two carriers?
LCY seems to work for niche traffic to larger corporate banking centres in Europe, rather than secondary (Belfast, Cork) and tertiary cities like Exeter, Dundee or Ronaldsway. The traffic is corporate deal focused so FlyBe will really struggle to break into this segment.
They are also generally unknown in London and don't share the same brand awareness of BA or Easyjet for the leisure traffic from the capital.