I think a relatively simple yet fun away to rework the Elementalist would be to have them gain constant passive buffs to their statistics based on their current element. So that, instead of Elementalist having to pick specific elements they can use effectively, they can use all them decently but excel in specific ones.
So like, if they're attuned to water they gain a significant healing power buff, so that they can heal a decent amount with their abilities even if they don't have healing power investment. If they attune to earth they get a buff to toughness so they can absorb damage similar to a tank, then fire provides power and lightning maybe precision.
The idea would be that the elementalist is able to switch its playstyle on the fly regardless of its gear statistics by just changing elements, but it needs to invest in specific statistics and use specific traits to be able to perform roles as well as other classes that specialize in them. So without any healing power investment, the buff while attuned to water allows them to heal decently but if they want to heal as well as something like a guard they'd need to actually invest their gear into it. Yet at the same time, with all their gear in healing power they would still be able to switch to fire or lightning and deal acceptable damage but not as much as a full on damage class.
The buffs could scale based on how much of that statistic you already have, so if you invest all into one the buff won't be as powerful so that you can't make like an ultimate built with infinite damage or healing or such. They could even have you receive debuffs to your other statistics based on your element, so you literally have to change elements situationally based on what you need.
The elementalist would become like a versatile master of none where they can fill any role acceptably and then can choose to be better at a particular one for specialty. Right now it seems like the elementalist is incomplete, they have the abilities to switch to any kind of role they want but the gear statistics in this game don't allow them to properly do that. If the elementalist gained buffs per element that allowed them to fulfill any role decently, alternating their elements would actually matter outside of cycling through attacks since each element would change their playstyle instantly.