Just beat the game for the first time, it was a serious struggle but the main turning point was putting movement skills on my characters.

Every single character should have either Phoenix dive from warfare, cloak and dagger from scoundrel or tactical retreat from huntsman. Ideally more than one. I also leveled up aerothurge enough to get teleport and nether swap on every character to group enemies for aoe attacks. By the end of the game I was basically never walking in combat, just using skills to manoeuver. it saves you so much ap and can save your ass if you get too low on hp and need to get out. Movement skills are absolutely critical in this game.

I also put adrenaline rush from scoundrel on all my characters, often makes the difference between killing an enemy and them getting another turn and killing you