I think OP hit the nail on the head.

I've been talking about this with my LS and they agree that GLA is better because it can sustain itself better. In terms of kiting, GLA gets access to Featherfoot, Second Wind, Decoy, and Sanguine Rite. I would take these abilities any day over Holy Succor, especially since you are now required to completely stop moving to Cure yourself.

I also feel that Spirits Within has too long of a recast. If you compare to WAR, Steel Cyclone has a 30 second recast and finishes their "tanking combo" (Heavy Swing > Skull Sunder (increases enmity) > Steel Cyclone) while GLA and PLD only get Fast > Flat.

Cover is underwhelming in general. It needs a shorter recast or the ability to block all attacks for a set duration to be useful.

While PLD with ballad is pretty good at surviving in straight-tank situations, I think the larger HP pool, better DD potential, and threat generation of WAR make it the better tank especially with how good of a healer WHM is now. It also doesn't require a BRD to put itself in danger to stick ballad on the tank.