The whole basis of the Eastern operation is that it is not competing against anything other than a slow and expensive train network. Its use of the Jetstream is perfect for the routes that it serves, but if FlyBe come along, with nearly half the seat mile costs, they can afford to reduce the price, and can usually afford to match the frequency to some level as well.
I’m sure there are one or two more, but the main routes they do compete on are those in which they still retain a significant frequency advantage, such as SOU-LBA, and SOU-NCL/ABZ. Once one or both of their Unique Selling Points (Route, and Frequency) are duplicated by another operator (currently mainly FlyBe doing most of that) then Eastern dont really have much choice but to pull out, as they have little chance of competing.
Their future can only be secured by ensuring that they remain on the routes that best fit their business model, and that essentially means niche routes with little or no competition. Which is what they appear to be doing 😉