That depends of course in what role you use a Cleric and what is "good damage" to you. For me the biggest problem of a Cleric is spell slot economy. In my Honour mode run I used the Tempest domain, Wet condition and Call Lightning for decent damage while spending few spell slots. In my current run vulnerability to Wet is removed and enemies (who are buffed by mods) are more difficult to hit than in Honour mode. Shadowheart is now a Life domain Cleric, like in the group the OP described. Her main task is to debuff enemies, the damage of Shadowheart therefore is much lower than that of my other chars.
The idea of the Staff of Cherished Necromancy is that you can cast Necromancy spells without using spell slots if you have Life Essence. Luckily the bug which allowed to use it endlessly is removed by Patch 6, it is a lot weaker and fairer now, so you can use the staff without bad feelings. As my Shadowheart is usually near the enemies anyway, she hopefully can greatly upgrade her damage with upcast Inflict Wounds while sparing high level spell slots.
The Mace of Lathander (my usual weapon for Shadowheart) loses a bit in Act 3. The two magic staves with Arcane Battery might be better under some circumstances (did not try it out yet) but one is usually for Gale, and the other is awkward to get.
