@zxcnm what rick is saying is that you dont need dex for cast time, but, if not for pvm only, you are going to be super gear dependant. On the other hand, when you are low level, lets said 100 or something like that, is better to invest on INT and leave dex alone if you have gear to reduce your cast time 100%
In your specific case you have 19% from KK and skull cap combo, 20% from staff alone and 30% from FAW so you are missing points yet, you have 69, so you need 31 to get instant cast. And if you thing about orleans gown you are adding 15% casting time, so basically you have 69-15, that being 54% so with 1 dex and that gear you cast is going to be super slow anyway.
I think that if you have the budget, get 2 RWC spell3/3 that will add 32% with both, so 54+32 will be 86%. You still can get 10% from temporal int with spell 5 so it will be 10% more, so 96%. Now ou miss 4% and that will be, i dont know, maybe a Dark Illusion carded mid gear. that will be 106% so instant with orleans.
Now, you can dish out Dex for other status that you prefer. Of course when you lvl up higher you will notice that even then you still can use dex for temporal dex boots bonus (0,5 reduction of fixed cast time) considering all your spells had 1 or less fixed is super op buff, specially for bio 4 leveling. And for some instant cast builds that dont rely on summons (because you cant always had ventus out). Of course if your goal is WOE i dont recommend going for 1 dex because, that will make you super dependant of gear and to be honest not a very wise option.
Anyway, summarizing at your level got int and get instant cast gear, i give you the calculations above, after that and when you use more your sorc, switch to whatever you want, personally i got on my woe sorc 120 dex, and on my pvm sorc too, because i like fast cast, and being more summon free (i like to mvp with my sorc so being able to defend myself or tank stuff or whatever, take priority over ventus sometimes.