with 0 spellweaving, you can cast Thunderstorm against 120 magic resist and give the target(s) the reduction to FCR (-6), but your chance to succeed is affected by the target(s)'s resist. i'm not sure how, exactly. you definitely have to use a circle for range, damage, and duration, and max duration is like 11 with a focus of 6, and resist does not change duration. Thunderstorm always reduces -6 FCR when successful (success does not mean damage alone; you can succesfully cast the spell for damage and not curse the target(s)), and the target(s) gets a debuff icon. the skill of SW might effect "hit" chance, but for the most part, SW skill seems only to effect % to cast. I think with 50 SW you can cast Thunderstorm 100% (min 10). if you have more than 6 FCR, like, if you somehow had a scrappers, a chaos shield, an inquis, and a 1/3 ring and a 1/3 bracelet, for a total of 12 FCR, your FCR would never drop below 6 FCR, and therefore, you would never be effected by Thunderstorm's FCR curse.
with 52 spellweaving, you can cast Essence of Wind against 120 magic resist and give the target(s) the reduction to FC (-2), but your chance to succeed is affected by the target(s)'s resist. i'm not sure how, exactly. you definitely have to use a circle for range, damage, and duration, and max duration is like 10-11 with a focus of 6, and resist does not change duration. Essence of Wind always reduces -2 FC when successful (success does not mean damage alone; you can succesfully cast the spell for damage and not curse the target(s)), and the target(s) gets a debuff icon. the skill of SW might effect "hit" chance, but for the most part, SW skill seems only to effect % to cast. I think with 92 SW you can cast Essence of Wind 100% (min 42). if you have more than 2 FC, like, if you somehow had a scrappers, a chaos shield, an inquis, and a 1/3 ring and a 1/3 bracelet, for a total of 4 FC, your FC would never drop below 2 FC, and therefore, you would never be effected by Essence of Wind's FC curse.