Too many cooks!
It is a two man cockpit, for heavens sake. Let them work accordingly. If you bring in the incoming crew (you barely ever meet them), the augmenting crew (their in everyone's way, having no place to go), any administrator (that couldn't be bothered by anything else but the next cricket match) or any kind of remote computer/laptop/calculator/adminstrators handheld prodigy, with programming that defies Windows 95 with a 386 processor, then you're heading the wrong way.
Too many cooks simply spoil the meal, especially those who know little about real cooking, if you get my drift.
It should be entrirely left up to the two operating pilots with the final loadsheet, provided mostly 10-15 minutes before ETD. The TO calculation should be done together and only then, with the actual loadsheet and the actual numbers and (most probably) actual runway and its conditions. That may sound late, but having done all the preflight preparations, the last 10 minutes should be calm and reserved for these crucial calculations and inputs, and subsequently adequate and specific briefing. The operating pilots should throw out ANYBODY during this phase, even including the augmenting Captain who has 30000 hours more on his cap, is TRE and comes from the land that invented better North Atlantic crossings than Lufthansa.
Any calculations and endless briefing-blahblahs done before are useless and dangerously mind pre-setting, as we subconsciously tend to thinks "it's already done".
I tend to go for fighting distractions, as a main ennemy before take-off.
As it appears in this incident, some distraction was "self induced and augmented" and might have accelerated resignation. We will see ....