Great addtional info! So things are pretty clear now. The high death toll seems logical now:

1) the escorts did not fly but were too far away escorting Ju52s.
2) Werner Stefan changed course and flew the Gigants closer to the allies instead of following instructions and make a detour.
3) the rescue Staffels were warned far too late
4) bad weather caused many survivors to drown

Found another Gigant view for you

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