Should I point out that the event was already run once earlier this year?
Perhaps that's the reason for it. You may only be getting one week of it now, but altogether in 2019 you'll have gotten it for a full four weeks. Think of this like a bonus to the earlier run.
This boss is actually funny. It had the fire wall as part of the fight something like three years ago, as well as a dude that heals the boss and one that stuns you. Then some update somewhere broke this and the boss was basically free. Now it's working properly again and people are complaining that it's too hard.
nexon hates f2p and they want to make it harder for them so that they get more money but in reality we will just quit.
Then do it. Everyone threatens to quit and walk away when nexon does something like this, but they keep playing anyway. Why should they care about people threatening to quit when the threats are as empty as their promises of transparency?
It's 10% per hit, so it's not really "high percentage". The problem comes in that there's almost no invincibility period between taking hits, so you eat two or three 10% hits in the span of a second.