Well half the catchment area for each is County Durham and you can get to either airport in pretty much the same time so yes there is considerable overlap. I suspect flights to Aberdeen are almost all work/business related and so aren't terribly price sensitive. Timing is far more important. The size of the market is driven by the state of the offshore oil and gas (and now renewables) industry - it was pretty dire from 2013-2021.
No-one is building a new regional aircraft because no-one is buying them - in W Europe anyway. Just about every destination can take a 737 or A 320 these days and they wipe out anything smaller. In places, such as parts of N America, Africa etc, Far East something like the ATR makes sense as you are more dependant on regular air travel to small airports. In most of W Europe you have good train and highway access