So everyone gets scaling mage armor or bark skin?
Fighters can benefit from spells like Mage Armor too. I feel strongly Mage Armor plus a Cantrip should be a Fighting Style. It is meant for Eldritch Knights to feel magical at level 1, but other Fighter character concepts might want to choose this Fighting Style too.
(Note, in the UA, Bark Skin grants temporary hit points instead of AC.)
Note, the spells
Mage Armor and
Shield are effectively force constructs, and
Shield of Faith is more like an aspect of fate that is scrying across timelines to navigate "lucky" opportunities in the form of a bonus to AC.
Each of these distinctive magical concepts might come imply other magical effects.
There are other defensive concepts too. For example, in Norse sagas the "helmet of dread" is actually a nickname for a magical technique, where one makes oneself mentally fill a target with fear in a way that makes oneself more difficult to be hit: a kind of Frightened bonus to AC.
The
Sanctuary spell is a similar kind of defensive mental Enchantment.
And so on.
I mean, that kind of works. But you'll still end up with every fighter maxing Str right away.
I have no problem with the Fighter class encouraging investment in the Strength ability!
At the same time, it is also viable for a Fighter to max Dexterity right away, rely on finesse and archery, and Stealth.
And it will be even harder to have any monk with any points into Cha.
The Monk effectively has:
AC = Wisdom + Dexterity
This wouldnt really change any when typically AC=Strength+Dexterity.
The Barbarian has AC=Constitution+Dexterity.
Since these characters would have to invest in three abilities (Strength, Dexterity, and Wisdom/Constitution), it seems feasible to allow them to wear armor if they want, effectively reaching upto AC 25 near epic levels. It needs more scrutiny, but in principle seems balanced.
It's hard enough for anyone to take the skilled feat as is. And your making it even harder.
The Skilled feat is a worthless feat.
Really, a half-feat (!) should grant four (!) Skill Proficiencies.
However, those feats that grant Skill Expertise are worth the feat (as long as it is for one of the more useful skills).