small part of the game where Radiant damage isn't literally the best damage type in the entire game...
I dont follow ...
What is so incredibly awesome about Radiant?
That almost nobody resists it?
Well ... that dont bother Death Cleric, bcs even those who do ... dont ...
So that should be 1:1
Or that things proc from it? Like orbs and stuff?
Well ... as you said, anyone can do that ... ergo, that is not a "light domain" thing ... i would even argue that Paladins, Open hand Monks, and basically anyone with source of Light and certain items can provide same bonuses much easier and more consistently.

So once again 1:1
Basicaly all Light domain gives you is infinite disadvatnage for attackers ... as long as you are willing to sacrifice your reaction ...
And fireball.
The rest of the game it can run around using Radiant damage with all the gear that makes Radiant damage really good
I dont really know about any gear that "makes Radiant damage really good" ...
All i remember are stuff that proc from it ... and even that are mostly just radiant orbs ...
Sure, there is that single Chest piece that gives Radiant nova, that is not a bad item i admit asmuch, still feels like it become obsolete quite fast ...
There is also that ring, wich gives you +1 Radiant damage ...
But something tells me that neither is what you mean by "massive".

And at any case ...
As stated before, even by you ... anyone can do that, ergo that is not Light Domain thing.
all the enemies that are weak to Radiant damage
Wich are ... ?
Bcs unless i remember something wrong, the only enemy that is actually vulnerable to Radiant are shades in act II ... WICH you labeled as "small part of the game" ...
---
Anyway ...
Personaly i dare to believe that Death Domain is worth trying ...
To me, casting cantrips to two targets for free, while ignoring resistance sounds fine ...
And once you get your hands on
this bad boy ... casting leveled super powerfull spells for free, while still ignoring resistance seems even sweeter.
