Why would IAG spend well over a billion Euros buying an airline to only shrink it?
It would be utterly irrational. Aer Lingus' current transatlantic network is far too small to be considered such a threat to BA that IAG feels the need to neuter it.
IAG will grow Aer Lingus, provided it can do so profitably. All IAG airlines are currently in a phase of growth. Indeed, Iberia has today announced the return of flights to Havana and new routes to Cali and Medellin. It wasn't that long ago people were claiming IAG was engaged in a vast conspiracy to shrink Iberia in order to prop up BA.