So, the argument is that safety can't be the airlines' #1 priority because it is subject to cost-benefit trade-offs. But stating that x is our #1 priority implies that there are also #2, #3, #4, ... priorities. For an airline these will include making a profit, delivering customer satisfaction, keeping staff motivated etc.
Now, if I can make a small improvement to my #1 priority, but at the cost of a significantly greater reduction in some lower priority item, it seems to me that I might choose not to make that improvement and yet still legitimately claim that it remains my #1 priority. Only if I reject the opportunity to improve my #1 priority because of a lesser negative impact to some lower priority item have I demonstrated that it is not really my #1 priority.
And I don't see that this has yet been shown to be the case regarding airlines and safety.