Agreed. There has been no problem with loads to Southampton. Yields may be another matter.
I suspect the aircraft could make more money on extra rotations to Birmingham or Edinburgh, although the sector time to Edinburgh may be too long to fill whatever gap is created by Southampton.
Another possibility is that with the tie-up of Stobart and FlyBe, they may transfer operation of the route to Cardiff to Stobart and sell through the EI Regional brand.