This is turning into quite an interesting thread.
AirportPlanner1's write-up of the Southend operations looks bang on the money to me - the jets were a disaster zone in almost every possible way.
As for "Zombie Flybe" the reason for the collapse was a lunatic CEO who had been told by "experts" (a couple of contributors on here spring to mind) who told him there was a fortune to be made out of LHR and AMS slots. There wasn't
There indeed wasn't, but I think the main person to blame for that was the investor who had a fixation on the Heathrow slots and being able to recover value from them - which was never realistically going to happen. It's not really fair to blame people on PPrune for that one when it was a hare-brained scheme long before anyone on PPrune got to ever hear about it.
There are definitely opportunities for unserved citypairs and routes that are being milked.
MAN-SOU was NOT, REPEAT NOT all business travellers. There was alot of VFR on those flights as well (including myself and friends quite frequently). Southampton is not an easy journey from the NW. Accessing Southampton cruises is also a factor. And business travel - whilst significantly reduced (as I said) - is not entirely extinct. Business travel is reduced, not dead. And not all business travel relates to office meetings either.
If we take SOU-MAN as an example, Flybe generally had 5 x daily services. Four of the five met the hub banks at Manchester with connections to ABZ, INV, IOM etc and also had connections from MAN via SOU to the French regional points which were barely served from MAN at the time. Between all of that, a chunk of traffic will be connecting which isn't there today. You then have a reduction in business travel - it's still there, but there's less of it. At very best, you might get to 2 or 3 a day in today's world when you strip all of that out.
That's probably the most obvious of the unserved routes and not enough to base a new business on. Yes, you have EMA-GLA/EDI - which Flybe had dumped anyway before ceasing trading - and bits like Cardiff, MAN-EXT and so on. What do you then have? A disparate bag of routes, none of which are a bedrock and with little or no operational or marketing synergy between them.
The other issue here is volume. If volumes on many of the ex-Flybe routes aren't what they were - and if easyJet are doing well at LTN, BRS etc then they'll fight to retain that traffic, and fight on price - then you're into flying smaller aircraft. You need higher fares to make that work. You cannot run a Q400, ATR72 or whatever is your weapon of choice at A320 low fares - you'll go bust (again) if you do. There's no middle ground between those things and if you think there is, that's where you build up a business and then easyJet come and sit on top of you, just as they were doing to Flybe 1 on BHX-EDI/GLA and they're now doing to Emerald, Loganair and others.
A great many of the comments here might be true in isolation, but I still don't see anything here which you could knit into a cohesive business which makes a profit. And that goes for ecoJet just as much as for Flybe 3.