Long ago (~12 years ago) I played through IWD2 with an all priest party (5 clerics and 1 druid). It wasn't very optimized but it still pretty much ROFLstomped through the whole game. Build stuff I can remember:
All shield dwarves
1 Tempus (axe)
1 Druid (scimitar / spear) (but I think she spent most of the game using that moonblade)
1 Morninglord (mace)
1 Painbearer (long sword)
1 Dreadmaster (Flail)
1 Lorekeeper (bastard sword)
Gameplay points I can remember:
- Early on, Sunscorch from the druid and Lathandarite was very important for blinding pesky spellcasters (and those drumming guys at the Horde fortress)
- Later, Animate Dead was very helpful; almost essential for the Raven monastery challenges
- It took a while to get good heavy armor for all the clerics, I think the final pieces came from those underdark merchants
- Holy Word was great, but it fried the Banite as well as the enemies, making him a suboptimal choice (Holy Smite as well, though it wasn't as important)
- Circle of Bones (and later circle of blades) were very helpful for chipping into enemies that 3/4 BAB folks had trouble hitting
- I was a cheap bastard, so I used the Lorekeeper's two Identify spells per day for almost everything
- I don't remember much about skills, I think I had diplomacy on the Morninglord and wilderness lore on the druid, probably just concentration for everyone else.
A much better "all full-spellcasting" party that I played with a couple years ago:
Paladin 1 / Painbearer of Ilmater X
Rogue 1 / Wizard X
Sorcerer
Battleguard of Tempus
Morninglord of Lathandar
Druid
These were all Dark Elves and they did end the game a level or two behind where a non-ECL party would; so lower CR doesn't quite make up for the ECL penalty (maybe because quest XP isn't level-scaled?). The addition of the Paladin level was mostly for the Holy Avenger, but the paladin dialog was cool too. Arcane spellcasters were less flexible than their divine counterparts, but it opened up a few cool combos like Animate Dead + Cloudkill. In the final calculus, I don't know that the rogue level was worth it; not many traps and bashing or Knock takes care of locks...
If one were determined to do an all-cleric (no other classes) playthrough, I would probably recommend:
Painbearer
Battleguard
Lorekeeper
3 x Morninglord
Lots of blasting, all good to take advantage of Holy Smite/Word, Lorekeeper identifies all the phat lewt.
Yes, it's interesting how the very first gameplay point you remember is the Druid. & is the only part about the early game that was notable while the clerics are all 'later'.
If I want to steamroll IWD2 then I always take 2 Clerics precisely because, late game, they can carve things up like a professional receiver. However, when I tried to take all six, I found it quite difficult to get to the later
As you say, it can be quite difficult to get good heavy armour for all the clerics & other such early inconveniences. But perhaps I just wasn't determined enough? Perhaps I missed a trick or two at character creation? Perhaps I didn't utilise them properly?
If anyone here can do it & do it well, the winner is the person to finish the Orc Fortress with the most gold.