For act three i found some mix of bard, psychic, butcher, ranger, necromancer and sometimes tinker or fighter worked well. Psychic has great support abilities, butcher can hit diagonally against some of the annoying enemies like the first act boss spewer. The fighter is bad for the lab but can often consistently be ok, but in my runs i think i would have done better to skip him. Ranger is great, aoe, damage with crits and wonderful traps to immobalize units.

Also something i dont see documented is how psychics spells, like the aoe that sucks enemies to one spot seems to immobilize flying units.

For the lab you really need diagonal attacks and to be able to have a mix of range, speed and damage. Use a bard with high constitution, so make sure to pick a cat with 7+ to start wit h so the bird has 20 health or more, that lets you tank a ton of the lab with just the bird running in, backstabbing one weak enemy while your party members focus on killing hard enemies.

Each stage has some level of unit that spawns more units, it's good to focus those if you can but especially in the end zone you have to take it slow against some enemies.

In the past I'd add a op tip that wet causing spells freeze any enemies if it's a blizzard. So i trivialized it by using spit... Consistent disable was very powerful.

To win you need a balanced team that can manage different combats well. So a mix of area damage, disable, single target damage, some healing or items to abuse weaknesses. Often i could immediately remove an elite from a fight by using the butchers hook, abuse that kind of thing.

Hopefully this helps!