I am not really deep into the strategies of dos2, i did beat the original sin 1 on hardest difficulty tho.
After about 25 houres of playing i feel like the new armour/magicarmour system is not really making the game better. I like that it reduces the random factor but the fights feel really strange since i won if i managed to reduce the armour to zero and i lost if i did not (during the first one or 2 turns). Health doesnt matter at all since i can cc them all day long (with spending only a small amount of ability points) if the have no armour left.
Since i not super deep into the game i dont recommend any solutions but i read some in this thread which already sound very good.