I think in these circumstances, it would not be unacceptable for the company to not pay the loyalty bonus to GB staff for a year or two. That way no one should be too unfairly paid or penalised.
However, as the pension difference has already been discussed, then this could also be the source of the compromise.
I also wish to add my welcome to the GB team. Being ex-Go too, I know how it feels and the 'resentment' takes time to fade, but it does. Ezy is a great company, as you will soon find out! Far from perfect, but a lot farther from the worst...