eyeinthesky,
why were the crews ... not able to look out of the window and see each other in those conditions?
Read the report carefully: They saw each other.
It is impossible to guess speeds and altitudes under these circumstances, as the report clearly shows (backed up by graphics).
Other avoiding action? Difficult when approaching at a 90 degrees angle. The good reasons for following the RA have been given in this thread. Selecting other/alternative measures means you are undermining RAs which are meant as the FINAL resort!