First = Rogue (Dark Weaver) + Cleric (Life) + Wizard (Green Mage) + Fighter (Mountaineer)
Second = Fighter (Sword Saint mod) + Paladin (Oath of Retribution mod) + Cleric (Battle) + Wizard (Shock Arcanist)
1) The first party was defensive in general, and the second party was offensive in general. But I think the second party was a bit easier. Damage amount per turn is also important for the survivability of the party because you could clear the dungeon faster. At cataclysm difficulty, because of huge HP of the enemy, low damage = too long battle = more chance to get hit by higher attack value of enemy.
2) Still, during the first campaign, Life Cleric was useful to wake up an incapacitated party member to good shape, and Mountaineer was helpful to enhance the general survivability of the party with his skills.
3) For the second try, two mod subclasses are really powerful. Oath of Retribution has Channel Divinity to restrain an enemy which was really helpful. Sword Saint has the power to bring advantage, and this was really great with a great sword.
4) The toughest battle during the entire 2 campaigns was the very first two side quests at party level 3. (I cleared them almost right after the moment the party reached level 3)Sorak sword piece and Goblin cave side quests. I cleared Sorak sword after 1 saves & load. But goblin cave side quests took 4 savescumming as far as I remember. I think the recommended level of these two side campaigns for Cataclysm mode may be better to be slightly increased, like after level 4.
5) The second toughest battle for both parties was Ghoul + Ghast ambush before (or after) Aksha room, on the hallway to the 2 bookshelves and one chest. No chance to ambush, battle begins from close range. (But if I grinded my party in the world map, perform multiple round trips between Dark Castle and Town to enter Dark Castle at a higher level, it would've been easy)
6) I only experienced a "dead" party member for this #4 and #5 battle and had to use revive scroll.
7) Very first Sorak battle was easy for both parties, but the Sorak Acolyte battle was a little bit tough, especially because of Sorak Skirmishers (ranged poison attack). Still, only cost 1 savescumming.
8) Dark Castle was OK except for the Ghoul Ghast ambush I commented on above. No tough battles. Aksha was also not terribly difficult for both parties. I killed all named figures inside the castle for 2 campaigns. No need to talk to bad guys :)
9) After the Dark Castle, usually party members are full of magic weapons and items (because of EA test purpose), so no more tough battles. Well, the battle right before the dwarven city (forget the name) against 2 veterans and 1 Darkweaver was not an easy one, but doable. 2 Veterans hit hard.
10) Up to level 5 (especially before Dark Castle), one or sometimes two party members were incapacitated during combat, like 30~40% of the battle, at least once during the battle. But almost all of these situations were not very dangerous situations. (Except battles I mentioned in #4 and #5) I was able to wake them up and heal them and continue the battle.
11) Related to #5, I cleared all contents but didn't reach level 8, and the game does not offer any world-map battles after I clear all available quests. It was a bit disappointing, I wished to grind my party further from the world map battle to experience level 8. I'm not worried about this part because this is EA game. So in the second campaign, before entering the dark castle, I grinded my party a bit to get more EXP.
I already suggested several posts about the difficulty of Solasta in the Suggestion forum, so I won't repeat them in this post. But I think Solasta is heading towards a proper and good direction and I hope to see more content in the future.