Chris
I think your point about over-supply on BRS-PLH is entirely valid. The cities are very close and CAA stats show normally only about 200-300 pax on the route each month, although for some reason there were 1337 in October and over 600 in November.
A quick random check of prices on Flybe's EXT-LBA and Air Southwest's PLH-LBA show the Flybe route to be around £20 or £30 cheaper on the dates I chose.
I wonder how much traffic there is for LBA from the southwest as a whole, and vice versa. From nothing we now have two airlines effectively serving four south west airports from there.
I reckon the sensible thing will be to see how things pan out this summer before either of the carriers thinks about whether changes are necessary. Hopefully, they will both do well.