Helldritch
Hero
Fortunately, this is not an errata but a "sage" advice.
Even in the DMG it is clear that SA is on wrong side of both logic and the game's mechanic.
The only case where I would allow a non proficient user from using a shield and getting all the benefits is when the non proficient user is using the dodge action. No casting, no attack, just dodging and concentrating on defense. That would be acceptable, but then, that character is pretty much useless in combat anyways. At least he can be usefull as a distraction for the enemies.
Even in the DMG it is clear that SA is on wrong side of both logic and the game's mechanic.
The only case where I would allow a non proficient user from using a shield and getting all the benefits is when the non proficient user is using the dodge action. No casting, no attack, just dodging and concentrating on defense. That would be acceptable, but then, that character is pretty much useless in combat anyways. At least he can be usefull as a distraction for the enemies.