Yes. Paladin is the only one that feels like a tank to me.
Warriors feel like they should be berserkers, cutting enemies in half with one cleave. Warriors in old Final Fantasy games, if I remember right, mostly used swords and shields making them more like tanks. Unless they were dual wielding. Later they also became breakers. They had abilities like Armor Break, Weapon Break etc. So while they didn't do the highest damage they had more utility.
Dark Knights have never been able to take to much of a hit regardless of how much armor they had. They normally had a lower innate defense stat to account for their higher damage. Their main mechanic was also sacrificing HP to do high damage. Cecil may have started as a Dark Knight but I don't remember him being able to take much of a hit while he was one. Even as a Paladin later in the game he was still one of you highest damage dealers. Tho since that game is a single player game you don't have much of a need for a traditional tank.
Squall was not a protector. He was a mercenary sent out to dispatch enemies of who ever had hired him. He could also be considered a soldier in the exam he takes. The gunblade it's self is designed not to protect but to kill enemies as efficiently as possible if the wielder is skilled enough due to the trigger mechanism. The gun fires blanks which cause the blade to vibrate at a high frequency making it cut sharper. Squall would have pledge to protect Rinoa no matter what weapon he used because of his out of no where love for her. Seifer may have been made the Sorceress' Knight but he didn't do much protecting. He gets beat rather easily every fight, and is mostly just used to... actually I never did know what he was used for since he failed at everything.
So yes. I do think Gunbreaker should have been a DPS and another job should have been introduced as a Tank. I do take solace in that at least it's not a limited job lol. (Sorry people that wanted to main Blue Mage)