[Autumn]

If the curses are LV5 then its -10 to STR/WIL/CEL/SKI/DEF/RES not -5

Regardless of the skill it seems the LV is much too high for those curses, and assuming these curses are lv3 with the usual duration you can simply chug a cleanse potion to get rid of the important ones, and your MAs will basically not even give a hoot about it, I fail to see the issue other than the numbers being tweaked too high, especially given that its a boss 10 star.

There are more powerful invocations that still ruin 1v1s like Spirit Pain, and ruin team fights like Earthbound Vengeance and Enma's Summons, Adon Graxis doesn't even benefit from HSDW or deal any damage so you can prevent the Hexer using it by just silencing them.

It just sounds like the OP is judging the spell based on spar etiquette in the arena rather than actually judging it for how much reward its impact has for being allowed to cast it in the first place, in a real fight where silences/cleanse potions/priests all exist and there's equal momentum impacts in the form of Sonic Shell or Quaking Heaven Kick which don't even need Gentle Embers rebia to support it.

This as an argument shows me this fact honesty:

Note: Your entire team using cleanse pots is not a viable weakness or option.

No but having it be a spell is, invocations can be interrupted with silence, damage used to be a way to interrupt them as well and I'd like to see that return eventually with a change to invocation talent.

To note, I agree with lowering the levels of the curses, it should be your skill rank of the skill again and not LV5 if this is true, as Rank 5 is beyond the cap and it applies all of them without the need to actually rank them up, I usually answer curses with a cleanse potion, its usually worth, and if you're afraid of using it in the arena then I don't know what to say.

For Fellel's Fumble and Plisfa's it should be have a max LV of 2 possibly, as these both are infuriating and very hard to counter-play against, in-fact curses in general are hard to counter-play outside of cleanse potion, but it still exists to serve as a momentum trade (Trading 3m for their 9m? Really good.)