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I'm sure that 4 clerics can finish the game with Craft and scribescroll. The only party that really can't get through the game is a party of 4 knights. Everthing else, can.
My point is if you want to finish the game with 4 clerics, don't surrender, is totally possible. (I'm not even saying that any party can with reloading a lot, I'm saying that any non 4 knight party can Ironman the game)
Again if you want tips on how to beat the Green dragon with 4 clerics, I can, if you want to use them. Though I would need to know feats and spells. Having Protection from acid is very important, but even without it, I think it's totally feasible at level 8. You can send me the save file if you want, I would find fun trying to find optimal tactics on how to beat the dragon with whatever you got there.

I still think there are a few encounters where missing arcane prowess will cause you severe trouble. Have at least one wizard in your party, and of course at least one cleric.
One of the best (ie most powerful) combination is 2 clerics/2 wizards. You can even do the spider fight at lvl4 without too much trouble thanks to plenty sleeps/sound bursts + coup de grace.

Yes, if you decide to use craft+Scribe scrols, no doubt, 2 Wizards+2 clerics is the strongest team, I feel if you play with scribe scroll and craft, knights are pretty underwhelming compared to clerics and wizard. However, I think no wizard is fine except for a very few encounters as you say, where I agree may greatly increment their difficulty without wizard.