Remove flame ground attribute for meteor to do a 5 fake multihit. This makes elementalist require pyromancer and it’s unhealthy.
Instead you might consider the following:
Meteor becomes neutral property, for each elemental buff from Element: Amplify attribute, meteor does an additional line for 50% of its original damage of each corresponding element for which you have a buff.
I would also change elemental essence i’d give it an arts that would be the following;
Elemental Essence : Mastery [Arts]
Focus on a single element in order to remove elemental penalty by 10% per skill level (up to 100%). Additionally, every time you cast a skill of the chosen element, you gain a stack of Mastery. For each stack of mastery final damage done with the element of choice is increased by 5%. Whenever you cast an element which isn’t the one chosen beforehand, all mastery stacks are removed.
In order to choose a mastery simple make it like the healing wheel, Top Fire, Left Ice, Bottom Lightning, right earth. Makes elementalist a class of interest for any monoelemental build; Terramancer, Cryomancer, Pyromancer…
On the other hand we have meteor which will benefit from being multielemental. Additionally Meteor arts could be changed so that instead of doing extra hits, meteor causes a debuff on any target hit;
Astral Burn; +50% dmg taken for 10s
Astral Freeze; 3s Freeze, - 20% dmg done for 10s
Astral Stone; 1,5s Stun -25% mdef and pdef for 10s
Astral Shock; 5s silence, debuff: take +10% damage from all incoming sources as a new line of damage, 10s.