Is it viable to tank with heavy armor without the Quen shield?

Solution 1:

No, heavy armor will reduce the damage you take (due to higher resistances, not because of a higher armor value, e.g. Grandmaster Ursine has 44% pierce resistance, Grandmaster Griffin 35%). But no matter what, you are not supposed to tank hits of enemies, you are supposed to parry or evade attacks, avoid taking damage whenever possible; that's simply how the game is designed. Quen allows you to circumvent this somewhat, but can create a dull experience.

On high difficulties, you will take a lot of damage when hit. Heavy armor will allow you to survive one or two more hits compared to medium, that's it. It also won't do anything to prevent a stunlock. On top of that, stamina regenerates slower in heavy armor.