As someone who has capped both cleric and fvs on the same character with very similar gear, here are some thoughts...
What do clerics get that fvs do NOT?
Advantage #1 Clerics get more spells at each level
Rebuttal: At no spell level are the fewer spells of a fvs a major issue. There just aren't THAT many good spells. Only issues are lvl 9 (3 of implosion/true res/energy drain/mass heal), level 8 (3 of holy aura/mass cure crit/symbol of death/mass DW) level 6 (3 of BB/heal/cometfall/mass cure mod).
All other spell levels the 6 spells that clerics get is absolute overkill. Almost always end up slotting something that is never cast at all.
The strength of the cleric is versitility. Versitility is near useless as many divine spells are garbage.
Advantage #2 Radiant I and II are great sources of healing.
Rebuttal: They are. The aura is a nice way to keep people topped up during long quests, and the bursts are a great mass cure. However, burst healing is what is more important, and FVS are equally good at that. Mass heal is such an efficient way to heal that it's the best course of action in most cases, and fvs can do that for longer. There aren't THAT many quests at endgame where the aura shines. Most have shrines every 5-10min.
There are very few situations where a cleric is a much better healer than a fvs.
Advantage #3 Clerics can turn undead
Rebuttal: It's pretty useless at endgame. Where are all the undead? It's generally better to use turns to heal/burst the undead anyway.
Compared to what a FVS gets...
-capstone 10 DR
-3x 10 stacking energy resistance
-weapon enhancements
-+6 refex saves
-wings
-700+ odd sp
-capstone free searing light/cure light wounds
-up to 50% more divine punishment damage from AOV and -50% FORT. That is HUGE, particularly with the new boss fort. Bring a fvs, or the rogues are useless....
-+2 spell pen/DCs/to-hit on debuffed mobs
-lantern archon
-30% extra damage on untyped/fire/physical spells
...think I got everything?
Solutions?
Spells-Improve the weaker choices at each level to make the 4th, 5th and 6th options something that is somewhat decent. Give divines more than 5 choices for 9th level spells! Make fvs at least SOMEWHAT regret the lack of those spells slots. They ought to be trading SOMETHING-I know sorcs at least feel slightly less versitle than wizards. Fvs do not feel that way in the slightest.
Presige Classes-Finish Rad III and make the other two prestige classes at least sufficiently powerful to make AOV FvS go "hmmm, maybe..."
FvS SHOULD be more powerful than clerics as they are harder to unlock, but they should at least somewhat close...
I've probably ticked off a lot of clerics by posting this but anyone who has capped both a cleric and a fvs knows that they are barely compareable.
And I'm not looking for a fvs nerf either. People need more reasons to play divines.
Just SOME of those reasons should point towards cleric over fvs. Right now that isn't the case.