Some history on Sins throughout official. When Wemade implemented the class the rest of their playerbase was already into their 70’s level wise, probably nearing 80. We had 2 full episodes of content dedicated to the first 3 classes, there was a status quo of sorts.
In order for anyone at all to want to play a Sin and also to allow them to catch up, Wemade made them very powerful and ditched all the traditional levels where items/weapons etc would drop, they added in twice as much kit for levelling Sins as the other classes had. Skills were able to work on higher levels so they wouldn’t just get raped by the existing playerbase while levelling.
That situation worked, the long established players and the newly born Sins were somewhat balanced. Until they caught up! Nearling the end of Prelude to War (Episode 3) when Sins had caught up and got items they became the dominant class. Many patch cycles ensued with many changes.
Episode 4 came around and subsequent patches also added more, instead of gutting Sins entirely they reworked most of the game. All skills, items, monsters, bosses, exp curve, everything received a review and most were actually changed. The Chi System was introduced and all the skills that came with it, this offered all the classes a more even playing fields and further defined each classes individuality.
The Sin has always been a difficult system to make work correctly. It is much like Death Knights and Demon Hunters in WoW, they come in incredibly strong to make them appealing against established playerbase, but eventually that overscales and you have to tone it back.
I’ve not played a Sin here, but from all the reading it feels like you’ve had a lot of the early game advantage, then a lot of the late game gutting without the benefits of the redefined balance the Koreans introduced.