Ace - I agree, a DEC should be given an accurate reflection of what his actual salary is likely to be at the start, and in this case it won't be anywhere near £82k, £50k is nearer the mark for as year 1 DEC on the 400. The ad is typical Flybe marketing speak - not an outright lie, but not really true either, they're experts at that!
Given your experience and the desire for this to be your final career move, DO NOT go anywhere near Flybe, you'll regret it for sure. They are an excellent airline and provide some good equipment for someone starting their Commercial flying career, but for experienced types....
There are a few exceptions of course, if you live within 10 minutes of a Flybe base and looking to maybe move to part time working as an initial step towards winding down your career, then it's worth considering, but otherwise don't even think about it.