The only real time when somebody from my party was tanking was back in fort Joy. Beast and Co. had just emerged from the prison dungeon and were happily striding up the wooden scafoldings when they encountered a whole upper courtyard full of magisters. That's the place where there is a tent and two wooden fences with a small opening in between in the upper section of the fort, next to the main gate. It was the only such fight I had in the whole of the game, with Beast blocking that small path and taking the heat. Later on I respeced him for a full blown out strength monster, cuz who needs constitution.
Playing through Pillars of Eternity after Original Sin 2 made me appreciate tanks so much more ;D. Yeah, I think that the whole of the OS2 combat design just doesn't come together very well. Just my 2 cents.