I was looking at the CAA stats and they might give Loganair some confidence about moving DND to SEN...
The Aberdeen route from LCY carried 3,263 pax in May 2018. This year Loganair’s new SEN service carried 2,411 after starting on May 12th so on average load that equates to 3,568 across whole month. That is the equivalent of taking all LCY’s pax AND finding themselves a few more. Of course it’s early days, but you’d naturally expect what is effectively a replacement route to what is perceived a distant airport to attract less people in its first month, not more.