I think the lore book(s) have mention of which calamity was which element, including the seventh. As for which element that was...

Shadowbringers spoilers:
The 7th calamity was all elements tilted towards Astral, and as we find out in Shadowbringers, Astral is Darkness. So both videos are correct. Astral/Darkness being the 'aspect' of growth/activity/chaos is why things went funky with the orange over-aspected crystals and such.