What, exactly, is the threat to Irish airspace? The only possible one is Russia
You obviously haven’t read the post and links above.
The primary concern is flight safety with non-transponding Russian bombers transiting their airspace and with no primary radars.*
That could be solved with the installation of primary capable radars and an agreement with NATO on the provision of early warning. Hence the quote of 3 radar systems at about €20M each.
The secondary concern is from hijacked aircraft as in 9/11 where they might wish to escort and/or intervene on any such aircraft within Irish airspace - which is where fighters come into the equation.
There is no mention of a war fighting capability.
(* Accepting it’s over 25 years ago, as an AD controller running Northern QRA intercepts from Buchan, I am aware of at least 2 MISREPs from QRA fighters following Bears west of Ireland reporting them as being co-alt or no more than 500ft below transatlantic traffic and passing within a few hundred yards of them without any obvious avoidance action.)