The standard revelut account (free) charges 1% fee for transactions above €1000 on exchanges. This probably has a bearing on the rate you paid as oppose to the AIB one.
To clarify, I added the funds via the Revolut app using Apple Pay, effectively "pulling" the transfer from AIB. I have always selected EUR as the denomination but this time it was GBP.
I am assuming the FX conversion would be carried out by AIB, however, perhaps this is done by Revolut?