I do not pretend to be a pro. I'm not. That's not a pilot question. In life, whatever the job you have. When one parameter is vital for you and you don't have it anymore you have to evaluate it.
My thinking is when you do not have anymore reliable IAS, how do you evalute it ? Which clue do you use to evalute it. If not GS, which other do you propose ?
What did source of information they can use to evalute IAS : Ground speed and that's all.
Of course the range of possible speed is narrow at FL350. So, why to pitch-up ?
One wind can be fastet then 75kts, so descend... or praise for it to be less than 75kts but you have to set-up a strategy to replace the automatic pilot and pitot/mach meter did.
Why did they expect climbing to FL380 ? To my knowledge atlimeter was OK. So they should know what they did climbing so high.
Other pilots have reported to live comparable IAS disfunction on airbus and do escape.
Sorry but I do not understand why they do no exploit G.S.