I should probably have mentioned that historically, plate was almost (when I say almost, I mean like 1:10000 odds) never worn on its own, and was usually paired with a gambeson at the least, and mail on top of that if the soldier was quite rich. That gambeson would help disperse the force of blunt impacts, making the plate ever more effective. However, if your character wasn’t wearing a gambeson or other thick garment underneath their plate, any significant blunt trauma should comparatively hit a lot harder. T-shirts won’t cut it, a thick jacket would be needed. Though, most people get emergency jackets on day one, so that’s a non-issue. Still, the kinetic energy from, say, a hulk’s punch would likely be far stronger than some dick with a club. It’d be preferable to nothing, but you should not be walking away without a decent injury if that hulk manages to get its hands on you.