Excellent debate of the various perspectives.
My guess here is that there probably more to this than seems obvious. If they can start an airline and secure the LHR slots that's a good foundation in terms of an asset and security. However, I've been around long enough to see how cut throat the industry is. Yes they may well have a sporting chance on the cost base side, but they'll need scale to generate cash to keep them in the game, and strong cash reserves to capture any sizeable network and win out over the competition who will fight their corner.
If I were a betting man I'd not fancy the odds.
In relation to Loganair, they have a sizeable fleet of regional jets that most likely will have significantly higher unit operating costs compared to a prop.
Southampton might have been a huge base, but I'd take it as a given the a low cost airline will secure a base their as soon as the runway enhancement is complete, feels like an easyJet space, though Wizz might move quick to secure it. In such an event Flybe2 might not get the same opportunity. BHD is wrapped up between EI and LM for comparable routes and in that market Emerald will be asking soon with a clean sheet cost base so not a quick win for Flybe2. Hard to see where the key market or operating model would be at.