i think it would
1. overpower marignon which has it as starting spell and already good enough against undead / demons . the holy damage already exists in form of the holy spell smite demon this is enough .
2. if it would be really so powerful it would imbalance the whole game especially if the damage would be (14+2d6 oe)x3 as caine supposes in his possibility 2 .
if demons further on even couldn't get fire immunity via items it would be really unbalancing.
if it is made holy damage instead demons / undeads should be given the ability to get 100% holy resistance too.
and for thematic reasons the arch demons / undead/devil pretenders should start with 50% already or even 100% .
because they are so evil and strong that they should easily find a way to protect against unimportant holy units like priests.
for dominions 3 it would be cool if powerful creatures like pretenders or arch demons would be 100% immune to everything which weak units cast / do .
e.g. poison from a poisonslinger does not harm any pretender .
but if another pretender can inflict poision damage against this he needs protection via e.g. items.
there could be 3 resistance levels :
against lowlevel units like poison slingers , lvl 2 priests ...
against midlevel units like mages with pathlevels from 5-15 , priests with holy >4 ...
against hihglevel units like pretendergods , archdevils , queens/kings of air , water ... , mages with paths >15 ...
so a poison slinger e.g. would easily kill other soldiers via poison but do no harm via poison to a pretender which is very realistic in fantasy worlds i think
