Any airline that invites you to an assessment and you make the effort at your own cost to go there and do their assessment as THEY NEED you and YOU NEED THEM - the key part is that they should respect those that make the effort to attend - its about being professional.
It is an opportunity for you to evaluate them and they evaluate you for fit. This industry has lots of supply for when there is demand so they are ABLE to treat you like Kak. When that airline treats you well and values you increases its own ability to differentiate against others that treat their employees or people like crap.
Run a fair process, keep people communicated to and plan this process - which can be a massive undertaking...and we do not understand fully their workload and ability....... but still you are empowered to do a good job and not a substandard one.
So there is a risk for them that some will accept if given the job and could accept another role with better conditions then them - so wasted time for them. But overall they all know the market and know their offer is a good one.
Sadly its their train and their process - if you want to wait for them fine other wise move on and don’t apply.
For me it is important for any organisation to run a process which is fair, transparent and on an even playing field. As it speaks volumes about you.
Frankly aviation is which has always treated its pilots like crap and will continue to do so - purely due to demand and supply
Those that slate Aer Lingus are only frustrated and will be singing their songs once accepted as people can be fickle...
Don’t put your eggs in one basket....
It’s just another company - who also needs you.. have more respect for yourselves.
Best of luck