Okay, I'm not to sure how to start and explain that what you created is great in theory, but feels a bit jumbled in execution.
I wrote some things down, that I hope do not sounds too harsh, as i do really like this idea. I can't at the moment but I'd love to retool it jut for fun.
The first thing I will state is that while having a Job that uses the Elements as a "base" design remember that FFXIV doesn't have a true element system so anything that deals with elemental resistance or damage is almost worthless, sorry to say; so skills like Element Cloak wouldn't do much but decrease incoming damage.
The second thing is that while being able to change/alter your elemental affinity is good, you have to remember that you have to keep it balanced, since most players will find the best affinity to use and possibly harass those who prefer to play with any other affinity. GW2 has specializations that use each element they have which is why their system can work, FFXIV as of right now have no specializations.
Also while the idea of Element I/II/III changing depending on your affinity is good, you have the spells themselves too "diverse" the coding changes that would be required to change each skill design would make the job to confusing and a bit hard to play. That being said having each tier being similar but having a different effect for say the AoE is fine or should be anyway. Remember you want to keep things interesting but simple.
You don't mention the attunement stacks until after every ability is listed, and they aren't really mentioned in the abilities either. We don't really get an idea of their purpose or what they are really for. Additionally, you have 6 attunements total, which might be a little much. 1 arching attunement or 2 attumements, one Umbral one Astral might be a bit better. As i stated before, people will look for the best abilities to use and right now your Fire skills are winning.
While the Water moves acting as healing spells is good, the potentiates are a bit off. Cure is 400 potency on any class/job that uses it but if the job has a poor mind stat the overall cure is rather low. So if this Elementalists Water/Cure spells mimic the other healers potencies the cures wont do much if their mind is too low. Additionally, you can cross class form 3 other classes, so probably Arcanist is out.
And lastly the Embody skills are a bit confusing. You indicate that they can be "reused", but any reusable skill has a short CD, these are 45 seconds long, the GW2 counter part only has a 10 sec CD. Also the buffs they give for using them appear to be too short and might not offer any real benefit to the fight. Additionally while the attunements and the skills that can be used change for a GW2 Elementalist, they also change depending on their weapon, FFXIV only offers one weapon, so that would play a different part in the FFXIV version.
Now I may of said all of this and it might seem mean or disheartening, but I really do like the idea, and I think it could work really well, it just might need some fine tuning so that it fits into what FFXIV is, but also is something new to experiment with.
PS. while I have never played GW2 I did watch several play-throughs of elementalists and looked up their skills to gauge what you were trying to present