I picked an enchantress and rogue my first time at tactician, and got slaughtered. The teleport didn't drop the skeleton on the others like I'd hoped, and the rogue's daggers and bleed attack weren't much good against 5 skeletons. 5 con each didn't help.
Since then, I haven't had any problem (I restart way too much). I take a wizard with summon spider, a knight with both knockdown skills, and a point of leadership on both chars for the initiative, and it's been easy. Other combos of characters were fine, but there are definitely some that are going to hurt, especially if they hit you both with the poison grenade, and you don't have a form of healing.
Later on, I don't think it's as bad, but then I use crafting and blacksmith to make sure I have good gear for my level.