if your cast time is that fast and youre pure magic even with a phen card it should be close enough to instant cast to not matter... 1v1 leveling get really slow later but you should be fine with your high damage fast casting... i dont think youd need to worry about dex unless for some reason you get divested.... then that would suck for your casting speed...
Oh, I have a Phen card in my accessory now, that's why I always have 16th night on, without it, the +25% cast time with the fixed cast time is unbearable, especially when using Flaming Petal. Now I want to take it off, but there's really no way to keep the accessory if I do that, and it'd cost a fortune to reroll a new RWC pendant, again.
And divested only happen if I go to WoE or PVP I guess ? xD, I'm not really into those things, since there are rumors flying around that ninja classes doesn't perform well in those areas, which is, the main reason I'm still guildless.
And I know, but I prefer picking on a target at a time I think, and that's why I've been doing repeatable quests as much as possible to avoid grinding.