I see BA proper as working on the Ts and Cs currently enjoyed, albeit with the potential future pitfalls. I would rather start from a position of relative strength, rather than join IAG on a reduced contract right from the very start.
I understand your points, but I still see the overall package as stronger than anywhere else, in my opinion. The other options that you suggest may appear within IAG are not appealing whatsoever, and I will be staying with my current company if that is what is offered to me.