That’s not really true. Aside from the Ein Sof HP increase and Healing increase through the attribute, you also get a wonderful synergy of Merkabah : Divine Protection attribute and your autoattacks.
Basically you get one additional autoattack line based on your atk (10%) + all factiors enhancing it (e.g. Blessing, Elemental damage).
You will also have a chance to block magic attacks and with the magic defence increement attribute you can further reduce incoming magic damage.
With the recent changes, Merkabah even had a CD time reduction from 45 seconds to 35 seconds(currently only KTest afaik) while the effect is available for ± 20-22 seconds (time until all 6 chariots exploded) with the slow movement attribute, so you have ± 50% of possible uptime, while the chariots also draw aggro for you, letting you ignore the aggrolimit.
What I don’t know is if Aspergillum recieves an additional line, since normally all skills cast are affected by Merkabahs Divine Protection attribute, so if Aspergillum counts as casting Aspersion, you might even get another line on top.
With Exorcise and Merkabah having a similar CD time(in the future), you have another synergetic option there for more damage output.
Sadhu and Kabbalist also have synergy, as you recieve a hidden amplification of OOB autoattacks via Double Chance and a doubled recovery rate on Praktiris HP recovery attribute (increasing the base value from 15% to 30% of your HP; this attribute is also affected by your increased recovery value through CON).
As Sadhus skills are also affected by the Divine Protection attribute, you will get another damage line on top of your Possession, which is pretty neat, especially if your atk isn’t that high and you got lots of additional damage (e.g. Blessing, Sacrament, other elemental damage[not tested if magic amplification affects the damage,too]).
Sadly, OOB autoattacks are not affected by Merkabah 
What I can’t test is if Sadhus Transmit Prana actually affects the bonus damage from Divine Protection, simply because I don’t have Sadhu C3 and Kabbalist C2 on the same character.
All in all Kabbalist is not so bad, it’s just lacking damage because the devs simply don’t want to increase the damage of the skill <_< ( I don’t understand the unfair mentality of having such a low multiplier that adds up to only 2700%; Let’s hope C3 gets an attribute to boost the overall damage).
The lacking synergy is currently only affecting a few Classes, but it has enough synergy for mixed builds.
Kabbalist C3 is still far away and unbeknownst to us (we get the impression from the datamined new attributes,though,that it won’t be so bad with multiple Ein Sof instances and Nahash to deal damage, curse and/or petrify enemies), so it’s hard to judge if Kabbalist C2 is really that bad of an option or not.