I've played through on hard without any generated characters, I picked a PC ranger. I have Eder, Durance, Kana, Aloth, and Sagani (barely). I did all of chapter 1 with just those 5, strategically I put a shield on edur and stuck him in defensive stance the whole time. When indoors or in a dungeon of any kind I would stick him to the right or left edge of a door frame, pull with a ranger. Run back through - he's enough to bodyblock the enemies (and out side of the teleporting shades) the enemies more or less queue up. Take Aloth stick him on the opposide side of the door, cast fan of flames. You can rotate the cone until Eder turns green, then barely back off it. Cast a couple fire cones, + his on encounter use stuff. I always open every fight of note with Blessing.
If you are out of doors, trapping or the spell equivalent can simulate control relative to corridors. Durance has a tier 2 spell called Repulsing Seal, you can cast it, set your tank in it - or go agro with your tank then run him right back into that spot. It will likely give you enough time to open the fight and get numbers down to keep him alive. Circle of Healing (priest tier 2 radiate area heal) seemed to be the most efficient heal assuming you don't need the spike, It is ae - but you must have the priest by the person who needs healed - which is fine, his staff hits decently hard as long as he isn't the focus of his attack target. Traps also work great in doorways you have your tank setup to hold in. Can slow down that initial spike damage to get enough rounds off.
If you haven't you should definitely set some auto pause features, Low endurance probably saves you more time than anything. I try to be as stingy with my spells as possible giving the camping restriction, but I prioritize using all of my per encounter abilities across all the characters.
Flanking really works and matters, if you can use the terrain to rotate fights your melee damage output will go up a lot. out of doors - its easy to flank wide, in a cooridoor make your tank hug a wall let agro settle around him then come up the with the rogue. If you have a second offtank option you can place them on the opposite wall to be a body block to keep the rogue free.
Spell wise, I have prioritized the debuff system quite a bit. The wizard spells I cast often are, Curse of the Blackened Sight, Expose Vulnerabilities, and Arcane Dampener. The first provides an AE blindness - its a circular ranged spell - easy to hit from safe positions. The second does -DR as that a priority stat for me. Arcane Dampener I use to deal with any encounter that has a lot of enemy spells. Anything to spike down casters. There are 16 Afflictions in the game, I'm sure there are easily other combinations that work. If you can inflict a few specific afflictions you can disengage without being attacked. Its a really useful tool to break your characters out of melee range when they are low health.
Another very good spell - if you lose control of a fight and need to save someone is the priest spell Withdraw. Its a invulnerability bubble and as far as my experience goes the character will regenerate to 100% before popping out.
I'm pretty sure rogue gets sneak attack damage on anything that's afflicted by an ailment or flanked - but I'm not 100% on that. The custom formations you can create are very useful. Speeds up combat a lot as my default formation is effectively how I want my characters spaced for any general fight.
