To me the only jobs that feel TOO durable are Paladin, Dark Knight and Ninja.

PLD and DRK because they can go invincible for 10 seconds which is just insane for how often LB comes up in Frontlines. They can disrupt an entire enemy team and you can't do anything about it because they're just invincible. IMO the invuln should just be changed to a very heavy shield (like 100% HP or something) so that it can be broken with enough damage.

Ninja because they have so many defensive and escape options it's ludicrous. It seems like almost nothing can stop a ninja from getting away if they want to. Between Shukuchi, Huton and Meisui it feels like it takes so much to bring down a Ninja.

I'm fine with the other melees. If anything, I would probably elect to slightly buff the defenses of ranged jobs rather than nerf melee defenses. Or if melee defense IS nerfed, it should be slight, not how it was before. When playing melee you need to be able to pop out of your team's blob to do anything (unless you're a ninja which is basically a pseudo ranged), but doing this makes you a target, and you need defense to do this without being instantly shredded. Melee DPS was borderline unplayable before the defense buffs because as soon as you separated from the blob of ranged classes you got targeted and bursted down.