Since you are planning ahead it will probably be right to assume that you want to consider all classes on the latest KTOS balance niveau.
Now what we have to consider for the choice are three things:
- Your team comrades builds
- your teams HP pool and recovery
- the content to clear
First, taking a look at Priest.
Priest will receive a huge boost in utility, just like Pardoner, since Increased Magic Defense and Aspersion will no longer be possible outside of party.
It has a reliable AoE healing skill, the ability to prevent death, the ability to resurrect comrades, the ability to instantly kill devil & mutant type enemies and Aspersion that helps reducing physical damage.
If you want to be mobile and have an easy time skipping oneshot mechanics, this class is the best choice. It can also help killing mobs in CM and Dimension Collapse with Turn Undead, so it’s a great help.
Next, taking a look at Paladin:
Paladin will become much more defensive and receive the ability to boost elemental and normal damage with Resist Elements,Conviction and Demolition, so it’s worth using it on a party with many Wizards or magic Clerics. Barrier can reduce incoming damage, Sanctuary has a decent defense boost in times of need, and Restoration is great as either HP or SP recovery tool.
Sadly, it focuses more on static and small area buffs, so the party has to stay together to receive all the benefits, which handicaps squishy classes that rely on their mobility to evade damage or classes in general that have to stay either further away or closer to the enemy to hit it.
It’s still somewhat possible to use it, but it would fare better when combined with Priest in case you need to survive some mechanic you failed because of the party being unable to spread out.
After the changes, Kabbalist became a somewhat okish support for most contents that involve attacking a single boss.
You have Ein Sof, which now recovers HP based on the targets and casters HP recovery, making it a more mobile version of Restoration, but with way less overall recovery.
It can be used for the whole party with Dievs Laima statue, because the CD and duration can be increased to have 100% uptime, but it’s very short-lived and the HP boost sadly gets halved as well, so it’s not as good as Paladins Sanctuary or any recovery skill in general.
Nahash also benefits from the new recovery effect when attacking, allowing some builds with high hit counts or fast attack speed to “drain” HP fast on their own; however, since the AoE is small, it has the same problems as Restoration, locking people into a small area, which is bad for endgame raids.
Tree of Sephirot also has this exact same problem, and the recovery amount was heavily nerfed by the latest changes to only amount to about the same recovery as a Heal (lvl 6 Heal = 665% x 1.1 [Kabbalist bonus] x 1.45 [Heal:Linger attribute] = 1060%; lvl 5 Tree of Sephirot = 10 x 103% = 1030%) over the course of 10 seconds, making you vulnerable for incoming attacks aiming at the area, while the damage received is reduced by only 20%.
This has a high potential if the enemy damage is already highly reduced by other skills (Counter Spell, Foretell, Barrier, Ausrine with arts), but otherwise it’s not a good skill to heal your team and can be destroyed easily as it is a magic circle.
Merkabah is a two-trick pony that was upgraded, but not in a good way. You have the damage boost and defense boost effect when standing close to the chariots (both boosts are 10%), which requires you to cast the chariots parallel to the enemy position to make the most out of the boost.
Sadly, this doesn’t allow you to make use of the new attack reduction effect on explosion, since the chariots will move alongside the enemy and explode somewhere else; on the other hand, if you collide the chariots into the enemy, you got a high duration attack reduction, but you cannot make use of the damage and defense boost for the most time, unless you’re willing to move away every time to get the maximum distance.
This also only works nicely if the enemy hates to move, so if it moves or is drawn away by a team member, Merkabah is not useful for its basic effect.
The second effect is introduced via the arts, allowing people who mount the chariots to avoid taking damage, with a separate 40 seconds cooldown. This is a nice countermeasure for wipe mechanics, but sadly Merkabah is not the fastest cast, so if you want to evade getting nuked, you either have to time it really well, or have to rely on luck. As the chariots are placed further and further away from the caster, it might even be problematic for the party to rely on reaching a free chariot in time.
Last but not least, there is Gevura, which provides both a damage boost and a cooldown reset against bosses. With Diev you have an easy 50% uptime, but sadly the damage boost is halved against bosses, so you can only induce a 15-45% damage boost for 12.5 seconds.
That also makes it harder to reliably reset skill cooldowns, as you have to hit 30 times within that time, so classes without several multihit skills will reset at best 1 skill every 24 seconds.
It’s also hard to keep track of hits in case you actually have many multihit skills to manipulate the reset to the skill you want to reset reliably for the best damage output, and skills that were reset no longer contribute to the hit count for CD reset.
All in all Kabbalist is a potent support, but it suffers greatly in case it doesn’t have access to both Oracle and Dievdirbys, so it is better as an off-support on a dealer build than a healer, potentially replacing Diev, Priest or Oracle.
However, the whole support greatly depends of the parties builds, as Gevura,Merkabah,Nahash and Ein Sof all depend on specific stats/skill mechanics to have a decent enough impact.
In your case, even if it sounds strange, I would try Paladin for a reliable damage control & support option, because your build focuses pretty much on magic support with Miko.
Priest is a good choice as well, but I would stay away from Kabbalist, at least for now, because it is not worth as much as the other two choices, and relies on many factors outside of your control (e.g. the calculated number of Notarikon for Gevuras damage boost, the skill set of your party, their actual HP recovery value and attack speed, their movement speed, the enemies abilities to quickly move or destroy ground target magic circles, your teams HP, equipment & defense values,etc).