PLD does have an identity. You're a bodyguard. You're sworn to protect corrupt officials, and we're sworn to bring them down.
Thematically, I think PLD is about supporting the vulnerable members of your party and intervening when they're in danger. Cover is probably the most iconic example of this, but some of the other support skills (Clemency, Stoneskin, Divine Veil) lend themselves to this as well. DRK and WAR, in contrast, tend more to disable their opponents to render them less effective at dealing or taking damage.
The problem lies in how we've interpreted PLD's identity as a community. If PLD is a "defensively-orientated tank", shouldn't PLD always be MT? If tanks are designed to be defensive by nature, then shouldn't the "defensive tank" be the best tank? But with three tank classes in the game, and probably more to come in the future, it simply isn't feasible for PLD to be the de facto MT in every encounter.
What happens when you build a tank job's identity around it being MT? There's no problem as long as this is the status quo, as it was from 2.0 up until Alexander Savage. But what happens when that changes, and (gasp!) two world firsts are done using a "non-standard" MT? You get an identity crisis, 5+ pages on the forums on how PLD is "broken", and an extended discussion on the "tank meta" and why "defensive-orientated" (read: PLD) tanks "can't compete" in today's dps-focused raids.
Here's the thing. Most people didn't sign up as a tank just to OT. So you have to learn to share. Each tank should have a full set of abilities that they can use as MT and OT.
Cover is a fantastic skill that allows you to extend the active tank's cooldown repertoire without requiring a swap. I'd like to see more tank abilities in this same vein about intervening during a tank buster to either counter-attack or help mitigate more damage. Support abilities like clemency and stoneskin need to complement rather than overlap with healer roles so that you can visibly see the benefit of your actions.
As far as actively tanking goes, I think that the change to Shield Swipe is a step in the right direction, although I'd like to see more oGCD based shield strikes.