As for the original difference between the A340 and B744 engine thrust.
The difference is mainly due big difference in total drag.
but, one must remember that the A340 has a much smaller capacity than the A340. Much much smaller. A B744 can carry 120 tons and has a mtow of 875,000lbs..A340-300 is only 41 tons and A340-600 only 55 tons..
Mtow on A340-300 is on 606,000lb ,A340-600 is 850,000 and uses 56,000lb engines.