I stand to be corrected but my understanding of the EU rules are that you are entitled to compensation unless etc. etc.
In other words it's up to the airline to show that circumstances were outside their control, not on you to prove it.
If they send someone to represent them then that will cost them money, and if they write to the court falsely claiming circumstances differing from the true events, then they are taking a risk that they will eventually be found out, which will not go without penalty.
I feel it is high time that the EU ruled that where an airline sells seats in the EU country where you live, over the internet, then you should be allowed to pursue a claim there, as that is where you made the contract. If, for example you live in the UK then you should be able to claim here, provided they have sufficient assets here to enforce the judgement, rather than have to sue in Ireland because that is where they are registered, even though they are trading over here.