ridiculous coding. I hit A twice and still killed. This game is beyond un-optimized and shouldn't need split second timing with this absolute shit engine.
It's always the same with the boss fights in TW1-3: They seem to be challenging as long as you don't know how to manage them. As soon as you find the king's way (or the king's ways) the boss fights get easy enough.
Btw.: It's no boss fight (it's a ballet of sorts) - but some kind of riddle: The player has to guess how he figures prominently in the choreography of the devs.
You need almost nothing - no potions, oils, no armor, no dodging/rolling - the cheapest silversword will do the job. The only thing which is very, very, very useful is the kayran trap - not as trap, but as signpost. Geralt knows exactly where he has to go.
So if you have real problems with the ballet then switch to "easy" and have a look at the appropriate video: With trap: https://www.youtube.com/watch?v=GqoWXx-IBRk Without trap:
Now you have to watch exactly where Geralt should cast Yrden. https://www.youtube.com/watch?v=BsXdXAx2aSk
On easy Geralt will not loose much of his health when a tentacle hits him! And if he casts Quen before, he will not loose any LPs, even in dark mode: https://www.youtube.com/watch?v=BB_O-3sbBQs