Yes, the airport staff have the greatest freedom to act here, though it is combined with them having to sort out the difficulties when things go wrong, people drop final legs and what not, hence occasionally their willingness to help may be nuanced accordingly. The temptation to just cancel your ticket would have been very great in some quarters, and I have some sympathy with that position.

As for the wrong BP, there were two parts: conformance and biometrics. Once you realised you had used the wrong pass then alongside that goes the point that you are not going to DUB unless you have a photo taken. DUB is a popular place for B2B, though personally I think there are better airports, but being in the Common Travel Area you need biometrics. And there is no easy way to get biometrics airside if none were captured in the first place. So what you should have done (a) ask on FT! and (b) get yourself landside again via the T5C transit and start again on DUB (that would be easy at that point) and (c) get conformance re-set for the longhaul once back airside, for which presumably you had more time to resolve. Had this happened you should have been back airside within 15 minutes.

If you had faced a re-price it would have been rather harsh given that you raised the alarm early, but equally there is a bit of me that says that if you are doing these sorts of trips it is important to be fairly meticulous about the details. I suspect you don't disagree.