CapnZapp
Legend
Why are you sidestepping the basic fact that if a player can trivially/cheaply attain the "cannot be hit" ability the game works (much) less well.I honestly don't think it is.
A few posters said it was utterly fine for a wizard with mage armor. Other posters have side it was fine for Eldritch Knights.
It seems the main problem people have with Shield, is when it is part of a highly defensive build that comes online about level 4. And, well, I'm usually not too concerned when "with this specific build they can..." arguments. Yeah, if you combine the right classes, feats and species with shield, you can make a character with very high AC. A level 1 fighter with chain mail, a shield, and defensive can start with 19 AC and that is nearly impossible to hit with monsters that have a +4 to hit. That's the point. That is what the player wanted.
Is it a little frustrating? Sure, a bit. But I play it up just like I play up my frustrations with the Barbarian just not dying or the rogue having a stealth result of 32 when they rolled an 8. The character is doing exactly what the player wanted, and if I truly, desperately needed to cause hp damage to a character with high AC who can use a daily resource to pump it higher temporarily.... Well, I think I can pull that off with minimal difficulty.
Why contort yourself around this issue when the simple (and correct) solution is to make it substantially more costly to attain this ability?
GMs should not have to work around a character that can only be hit on a 20. Characters should not be given this ability in the first place.