I think they will look at it on a European scale. Other EU countries are dominated by 1 airline (or airline group) as well.
On a European scale, this adds (based on 2018 figures) some 12m annual pax, adding to IAG's current 113m. They will remain #3 in Europe (by passenger numbers), behind LH group and Ryanair, and ahead of AF/KL.
If that takeover wasn't allowed, IAG will (rightfully, if you ask me) complain about LH having been allowed crazier stuff.
Don't get me wrong, I'd prefer the airline world being run by smaller, independent airlines instead of cartel-like groups, but the zeitgeist doesn't seem to agree here.
Ideology: The mistaken belief that your beliefs are neither beliefs nor mistaken.