The 3 sec was on Death March, ok maybe it's 4 sec max. He does take from 28.000 to 36.000 damage per second from Igni...
But I preperad, came to the island with a few potions of clearens, different gear and saved before the fight, so now I can have the fun of fighting him with every possible build.
Igni in the vanilla game is completely OP. I really don't know how people can play in that way. What's the good thing about killing a monster 10+ levels above you in 3 secs? It's obvious that Igni is broken as it is in vanilla.
Luckily there are mods that fix that (along the difficulty) but CDPR should also really (really) revisit some of the most broken skills in the game (as Igni). The rest they can leave to modders as I understand if they don't want to make the game overly difficult, but some skills are completely and uberly unbalanced in comparison to others and remove all the little challenge the game has.