Certainly true there wasn't much slack time for an Aer Lingus aeroplane. If it wasn't carting passengers or cargo about for its masters it was working for somebody else, as we've seen more recently with the Little Red A320 lease.
Did their 707s do much transatlantic work after the 747s had arrived or did they do like JAT did with theirs, i.e. charters and back-up flights ?