BA did absolutely the right thing here. Safety first and that's what BA did. Would have been a lot more convenient if a diversion to a BA-serviced station had been possible, but it apparently wasn't.

The key was to get the plane down safely, the pax off-loaded and then worry about alternatives. No coaches would seem natural. Also, wonder how many taxis there were at that point looking for a return to DUB and who would have located and paid them given no BA personnel and ground handlers presumably tied up with the next arriving aircraft.

Part of travel is having to handle things on one's own, as OP did. OP made a decision based on having to be in DUB by 0700 and will hopefully be reimbursed. But, under the circumstances, hard to imagine how BA could have made other arrangements without tying up however few ground handlers were around.

Bear in mind that it wasn't until the failed landing at DUB, that this entire contingency came into play. And, had a return to LHR or diversion to MAN been possible, what was OP's plan then? A much longer and wetter taxi?