The traffic numbers are not good for an Airbus, but ok if they are on an Embraer!!
Not really - if you look at the operating costs on a sector like that, a high degree of the costs are fixed. Heathrow landing charge, nav fees and parking for 45 minutes for an Embraer 145 is £787 and for an Airbus A319, £858. If you assume an average fare of £75 on those routes, it means you've got to carry 10 passengers on an Embraer just to pay the Heathrow charges which is 20% of your capacity gone before you can pay any other bills. For an A319, it's 11 pax per flight to pay the landing fees but this only equates to 6% of your available seats.
Running RJ145s into Heathrow will only ever be a damage-limitation exercise unless you have extremely high yields. Even Luxair had to give in on that one eventually.