D&D 5E Why AD&D Rocks and 3e - 5e Mocks all over AC...

[tetrasodium]

I like the idea of Crits bypassing DR, makes them extra special.

As to powering up casters if DR doesn't affect magic No, but Yes. No it doesn't power up casters, they do the same damage they are doing now to the armor wearer. But yes in the sense that the wizard's melee body guard is now doing less damage to the armor wearer. I think the simplest way would be to just let DR effect any source of damage. Then there is no debate on whether something is magic damage or not. In essence DR/turn would function as an non-magical temp hp source.

In the past DR had an elemental analogue in the form of resistance to energy. While DR was DR X/bypass condition resistance was resist X/ impacted element. Thee two worked together to balance out lots of smaller attacks/ DoT effects almost certain to land some or be an ongoing nuisance to a target compared to fewer bigger attacks with more riding on each.