As I read it, in this case, EI delayed ex-DUB so you missed your transfer onto an BA flight to HKG in World Traveller. BA arranged for you to travel on the next available flight in World Traveller. In the meantime (or beforehand) someone else had perfectly correctly reserved your choice of seat on-line for your re-booked flight, so you ended up in a less desirable seat but in the correct cabin.
In what way can BA be held responsible for any inconvenience and why should they
upgrade you?
Any issues you have with any loss or costs must be with EI.