I've found the FOS to be fairly useless in my dealings (other matters), but hopefully they come through for you.
I understand your point of view. In your case the introductory offer of the 80000 does make a big difference. Is it still in the following years?
My case is under investigation by the Ombudsman - while there is proof of misleading information also during the conversations with Amex reps ( told me minimum 3 months wait to apply for complementary card - which seems to be not true and followed by 6 months wait instruction etc.).
Will post outcome.