IMO The difficulty comes from having to evade attacks while performing the more concentration/skill intensive rotations. It looks easy, but actually requires some practice. Evading aoes isn’t always just stay out of the red circle, a lot are not possible to evade just by moving away, you have to use an evade skill or i-frame it.
You have to manipulate attacking tempo to reaching that high attack speed to Buy Blade And Soul Gold. And lot of skill combo like 2RF,3RF, and Pressure Point’s stage control,etc…
Unfortunately, KFM is not a high dps class(if you’re not expert), mostly he is tank due to his skill(Explosive Fist) will generates additional threat & restore 1% max hp, and has most(six) immune skills. You have to practice hard in order to reach same amount of dps of other class.
Worth of mention is in TW BNS some boss have double amount of HP than other BNS version(you can see in the video). That force TW KFM players have to play very well in order to defeat the boss.
Honestly its not all that hard. on the RU server i managed to kill the musin 8th floor (2nd and even 3rd boss). Even in the RU server the Q/E evasions dont have the same ammount of iframes as the KR has so it seems even harder on the RU server (aside from some of the AOE skills).
I think the hardest part comes from ur ping. If ur ping exceeds 100 ull lose out on DPS on a KFM. On the 3.0 patch of KFM to maximize dmg u can either 2>f>1>2>f>1… repeat to preform this properly u can either train like a hardballer or just macro it. Same goes for the more complex combos which could be. 2>1>3(kick addition when stunned)>F.
KFM has many animation-cancellable attacks..that’s why you need a very good ping (0-50ms) to be able to execute many attacks as much as possible in a short amount of time…[and you may need Blade And Soul Power leveling] (e.g. within 3 second of stunned/groggied enemy, you can already deliver 9 attacks (minimum) that could decrease your opponent’s HP by 20% in that short span of stunned time)..