Or you could have an all armor character be a guardian class that can absorb one hit above its armor. Or have the rangers have the 'trample' skill (since its the dmg dealers who are the ones who go over an enemy's hp constantly). Or have a diff kind of dmg option like a multishot that hits several targets.... just some other ideas
Consider having the paladin be something else. To me it doesnt seem like an efficient role. It seems best to have a big armor in the front since that is the first and only line of defense (once he falls, anyone with lesser armor will fall as well), and then the rangers and then the cleric. Consider having a different role with a different function. Perhaps a support class that can temporarily buff allies' dmg or armor.
Tip for finding the "perfect team":
The randomizer's selection is pooled from the monsters in the current area so if your looking for a specific monster and see it in battle, randomise in that area to get it.
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 "Tap Tap Infinity"){kind=icon}
 "Brute Wars"){kind=icon}
It'll be in the next iOS update.