Fliterider- the Thomas Cook debate was had before but as pointed out at the time their withdrawal wasn’t as simplistic as not enough market at STN.
Something your argument regarding Norwegian also misses is that had history taken a different course STN probably would have been their long haul base for London. Norwegian were well established at STN with a number of routes to Norway (this was before they extended across Scandinavia and onto the rest of Europe). LGW fell out of BAA’s hands and the new more nimble/bullish operator poached a number of airlines - Norwegian, Air Berlin (except Düsseldorf) and Air Asia moved across, possibly others. So had STN been more competitive, this debate could be redundant.
Its also fair to note that for Air Asia its foray into LGW turned out not to be the pot of gold compared to STN conventional wisdom and argument suggests it should have been.