Sad news for the staff, however Are Lingus has been trying to reduce staff numbers over many years and compared to other airlines is very "top heavy" staff numbers-wise for only 52 aircraft and 4500 staff. If you take Easyjet with 15000 staff for 320 plus aircraft and all the other "products" or Aegean with 2600 staff for 60 aircraft for instance.
The pension pot had holes as early as 2014 and if IAG had not stepped in, probably it would have been culled by Ryanair and numbers slashed.
Good luck to those effected, part time and wage reductions are much better than redundancies and considering the money wasted on Brexit, Covid PPE that was rubbish, Track and trace, it's about time for some rational thinking to save jobs.