what two Irish companies do
Those two Irish companies both trade and employ people in the UK. They're also both listed on the LSE. For that reason both companies fall under UK court juristriction.
As for the grounds for the original complaint, that you allude to... The IAG bid certainly hasn't blown the case out of the water!
Any company, including Ryanair would not be happy with their principle competitor being a major shareholder and able to disrupt the business.