I have a full suport Pally 3 -> Kab 1 -> Inqui (full con) and a Pally 3 -> PD 2 (full INT) and i’ll give you my input and personal opinion (pvm oriented):
Kab c2 seems to be in a pretty bad place right now for pvm. It has nearly zero dps, Merkabah’s invicibility is much worse than other invincibility options (i.e. Ausrine, Sterea Trofh), and while Ein Sof may be nice for boosting max hp, it’s still limited to only one person (and wastes one precious charge of your Heal to heal them to newly full hp).
For a full support build, I would prefer something like cleric 2 -> diev 3 -> druid 3 for Sterea Trofh, Ausrine and World Tree (coupled with those pesky Merog Shaman infinite safety zones). If you want to be very hard into support, pick full CON or a very high CON build so you don’t die.
SPR for a paladin is also a bad choice. I wouldn’t focus on SPR just for Barrier (and Zalciai).
Also, I’m not a big fan of full support builds. In pvp they work nicely but in pvm it’s just easier killing your enemies faster. Rank 8 clerics have some good dps options too.
If you want to stick to paladin 3, I would suggest PD 2 or something with Inquisitor. If you want to dwell hard into full support, you can ditch those two options and get Drud c2 at rank 8 to have Sterea Trofh lv 5 and Merog’s Safety Zones. Might still be more supportive and defensiveness than Kab c2.