How do you meet the accuracy requirement for endgame raids?

[Sapphic]

I dunno which videos you've been watching, but from the sounds of it, you're talking about T12. That massive DPS comes from the initial Whitefire inflation with Baned dots running for nearly full duration on three targets + the boss as usual (and Shadow Flare ticking on at least two Whitefires as well). This inflation becomes especially big if you get a 2nd set of Blackfires + Whitefires before the boss transitions into Brand.

Blackfires originally got a vulnerability debuff on them from whitefire so DOT poetncy was increased, then bane to the boss and those extra potency dots transferred so the damage on the boss was increased substantially, hence the changes to HP down on blackfires instead.