I suppose one could change the default AC calculation: 10 + Dexterity Modifier + Proficiency bonus. This would pretty much eliminate light armor. It might step on the toes of the monk and barbarian classes, though it could also reduce those classes MAD a bit. It would make the mage armor spell obsolete. Overall, I don't think such a change would be unbalanced, though I'm not sure it's worthwhile.

If, however, the OP is suggesting adding Proficiency bonus to all the standard AC calculations...nope. That would significantly affect bounded accuracy. Characters would miss more often, which would affect enjoyment of the game (the game system assumes a certain accuracy in attacks - that's why hit points are so much higher in this edition). One would also have to re-calculate ACs for most creatures in the MM, which is a lot of work. Overall, I just don't see adding Prof bonus to existing ACs as a good idea.

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