I can't talk for them but...
Unarmored Defense is worse than Light armor statwise unless it's 10+DEX+CHA and you have 14+ in both Dex and Cha.
It actually make MAD a bigger issue.
I did the Unarmoured Defence thing with the NPC Paladin Malenn of Mitra for my
Frazetta-influenced Wilderlands campaign. DEX & CHA based with rapier (currently
shortsword), shield and loincloth.

This wouldn't work with a 2-handed sword in 5e though since you can't use DEX for
greatsword attacks.
Here she is - she's the same NPC Paladin I gave Smites without spells as such.
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Malenn, Paladin of Mitra
Cohort (wife) of Hakeem Greywolf.
Human
Armor Class 18 (+2 DEX +2 shield +4 CHA)
Hit Points 56 (9d8 + 18)
Healing Dice 4 (d8+2)
Speed 30 ft.
Proficiency +3
STR 8 (-1) DEX 14 (+2) CON 14 (+2) INT 11 (+0) WIS 13 (+1) CHA 18 (+4)
Good saves WIS, CHA.
Senses passive Perception 14
Challenge 3 (700 XP)
Divine Sense: 4/day she can focus - as an Action - & detect supernatural celestial, fiend or undead within 60', but not mortal alignment. Can detect consecrated or desecrated ground.
Brave. Malenn has advantage on saving throws against being frightened.
Unarmoured Grace. Malenn adds her CHA bonus to AC when unarmoured.
Duelist fighting style. +2 damage with single one-handed weapon.
Actions
Multiattack. Malenn can make two melee attacks.
Blessing of Mitra 6/day: Recharges after Long Rest - requires prayer to the rising sun to recharge. Action, requires a sprinkling of holy water, affects up to 3 willing allied creatures within 30'. In the next 10 rounds whenever the Blessed allies make an attack roll or a saving throw they add +2 to the roll. A creature can benefit from only one Bless die at a time. Requires Concentration - this effect ends if Malenn is incapacitated.
Alternately she can use the same energy to Divine Smite on a hit for +2d8 radiant damage, +3d8 vs undead or fiend, this does not require holy water.
Lay on Hands: She can touch someone and restore up to 30 hp per day (or spend 5 hp to cure disease/poison). Recharges after long rest.
Weapons (2 attacks/action)
Bronze Shortsword ATT +5 dam 1d6+4 (+2d8 smite)
Unarmed ATT +2 dam 0 (+2d8 smite!)
Equipment: Altanian loincloth, sandals, steel-rimmed round shield, bronze shortsword with scabbard and weapon belt. Backpack.
Treasure: 688gp (188gp in backpack, remainder at Vex Villa vault for safekeeping).