I think taking this approach to its limit eliminates defender and controller as distinct roles. (Which may or may not be objectionable - I have no strong view, but the 4e design team clearly wanted to capture something they regarded as important in the legacy of the D&D fighter.)My rational for the idea of interposing something between the enemy and the mage's body is the fact the fighter does the same thing. Difference is, that mage build is using magic instead of armor
The reason I describe the fighter in my 4e game as a controller as well as a defender is with a reach 3 (polearm plus Eternal Defender) and many close burst 2 attacks (polearm plus an epic feat whose name escapes me) and Polearm Gamble combined with the fighter ability to end movement on a successful OA (and due to his WIS bonus he generally misses OAs only on a 1 or 2, and has a paragon path Warpriest feature that lets him reroll 1s) he can exercise a high degree of battlefield control without having to put his body directly on the line.
I think that is a major change (innovation?) of 4e. Though it also fits with some of my memories of name-level AD&D.In my experience, prior to 4E, if you were focused on drawing damage to yourself, it didn't matter if you were in melee or not or what class you were... you were probably going to die, so every time it happened was a special circumstance. 4E, at least for those I know, introduced the radical new idea that you could do that and reasonably expect not to die.
The fighter in my 4e game is a dwarf who has second wind as a free action (race plus feat) twice per encounter (feat) for two surges per go (Cloak of the Walking Wounded) with an enhanced surge value, especially when bloodied (Dwarven Durability feat plus some sort of magical Belt). So he is particularly adept at soaking damage, making up for the fact that the party's "official" leader is a hybrid ranger-cleric who has only 1x/enc Healing Word. The other defender is a paladin who has second wind as a free action when bloodied (Questing Knight paragon path), a ridiculous number of surges due to a magic item that lets him take surges from CHA rather than CON (Ring of Tenacious Will), and is not above using Lay on Hands on himself if needs be.
It's probably not surprising, given this, that I see the self-healing elements of the 5e fighter as consolidating a tradition rather than departing from one.