Harrogate - I am familiar with the concept, I was merely correcting the ascertion that Jet2 didn't market itself as low cost, which it does for the reasons you alude to.
In effect though looking at the routes/frequencies that they offer to some destinations i.e the Greek Islands isn't it actually incorrect to bracket them with the likes of Ryanair or Easyjet. Both of whom one would readily accept as LowCost Operators, when in fact what they are doing is block selling to tour operators and selling the rest of the seats themselves. A smart move in my humble opinion.
It's down to how you interpret what a low cost operator is innit. The original lo-cos were based on the American model, which was quite a rigid formula. They were point-to-point, flew to peripheral airports and, had single class cabins, flew direct, no frilly add ons, single aircraft type, etc.
These days, our lo-cos don't conform to many of those principles, so the term 'lo co' is probably redundant, or needs to be elaborated on when used.
With the advent of longhaul low cost operators, both on direct and indirect routes, the model is evolving again. In fact, it's no longer a model at all. It's more of an umbrella term that applies to most of the airlines that don't fall into the legacy or flag carrier categories.
You can look at Jet2 and say that they never actually were a true lo-co anyway. They've nearly always flown direct to major airports (apart from Leeds, ho ho) and they've always had enhanced services. These days they also chuck in the odd longhaul route, and operate more than one type of aircraft.
They clearly know that they're not a true lo-co, but they've rather cleverly paddled onto that wave and have had a lot of success in doing so. It's no secret to a lot of their repeat customers (of which there is undeniably a lot) that they offer more than a no frills experience.
So yeah, it's down to labelling. They're still a cheap airline in the general scheme of things, but they were never a 'true' low-cost airline, in the strictest definition of the term. You do get more bang for your buck with them in most cases, but there's only so low they can drop their fares, because of the fundamental fact that they're not flying to peripheral airports. So at least part of their fundamental business model prevents them from being a lo-co. You pay a bit more for it, but the trade off is that you probably fly to nearer you need to be in most cases.
Their lo-co style marketing of remaining seats on charter routes is not something new. Look at other larger holiday airlines to see how that's been going on a lot over recent years. But yeah - it's working for them. They're performing as well as any other airline at the moment, and considerably better than a fair few.