I can't say I'm a fan of the trend for "densification" but a large part of the economy market is hugely price sensitive and from anecdotal evidence the arrival of Norwegian has attracted a lot of interest.
BA is not a business to make rash decisions and they are based on the extensive data analysis, not anecdote.
I also don't buy the narrative of an airline in decline.
It wasn't that long ago that it was slashing its route network under "Future Size & Shape", its aircraft order book was empty, Gatwick had the axe hanging over it and the Heathrow operation would lurch from one (often self-inflicted) operational and
PR disaster to another.
The airline is expanding (having announced 10 new routes in October), carrying more passengers on more routes than ever before, and has found a path to something other than progressively shrinking and a "cut and run" approach to competition outside Heathrow.