MAG cannot plan for a 'Goldilocks scenario' alone as you would have them do. But if that does come to pass, they'll do fine. Just keep building full-speed-ahead.
Other major airports have exactly the same issues surrounding the timing of infrastructure investment and do not have outmoded and decrepit terminals. In many cases truly impressive facilities are provided that cities can be proud of and while Manchester can claim to have done this in the past it has now fallen too far behind through the use of patch and mend short term solutions.
Long haul having to wait for gates? Appalling. Great news for Dublin.