You're assuming Flybe and others pass on the reduction in APD to the customer.
Flybe ARE selling seats and don't have competition on most routes... why cut the price, a competitors big jet on most of our routes wouldn't work?
It's legacy overheads that are killing Flybe get rid of those once and for all and move on.....
Anyway I don't know how to run an airline just fly a plane so my opinion is pretty worthless in business matters.