With SCH being the dedicated shield healer, AST being the hybrid healer and WHM being the direct regen healer its time for another more heavily focused Regen healer.

Chemist would be the next Heavy healing Regen based healer with a few gimmicks to make their gameplay more interesting.

Before I get into how a chemist would play firstly we should decide how their weapon would function, ideally using just a vial would work but it would not fit into the multiple weapon layout of FF14 so they should use something more fancy, more modern.

Slight spoilers ahead


Weapon: Garlean Wristgun
This could easily fit into the world with things like MCH robots running around now. A hefty function wristgun with rotating vials at the side capable of mixing concoctions and launching easily breakable vials at enemy's or allies while also have the capacity to shoot out darts for potential dots would be a perfect fit for the game.

Story: self-exiled chemists
(concept, can easily be disregarded with upcoming story changes)
After witnessing the damaging effects of the black rose, driven garlean chemists now wander Eorzea looking to find the ultimate cure to the ailment to prevent further catastrophes while also sporting equipment to heal any ailment on the fly.

Ability concepts
1. Ninjutsu like mixture system for buffs and big boy heals
This could easily fit into how a chemist would work, the mixtures could be learned through the class quest and the effects should consist of highly beneficial but not **CRUCIAL**(for most content) buffs, dots, and heals.
Tying a dot with similar weakened effects to trick attack would be nice, for example a dot that lets a boss take 1% more but scales to 3% as the dot reaches the end of its duration, making for interesting gameplay for a healer.

2. Multiple regens
This class should feature multiple regens as a core of the class would be interaction with regens to enable explosive healing at the cost of sacrificing established regens.

3. Instant regen pops
This part will need heavy balancing far beyond my scope, but the ability to pop regens for their remaining effect(or something close to it) would make regen healing feel more interactive and reliable, similar to resto druid from wow. This also allows a class more heavily focused on regens to not rely on instant cast big heals that interact with nothing, separating them from WHM

overall I think we need more interesting healing concepts especially with the changes to healers in 5.0. Chemist in my opinion would be a breath of fresh air if they bring something new.

TLDR: Chemist would be a regen healer with ninjutsu(mixing)