Sub's lapsed and I don't plan on coming back so I needed to get this out get some closure, but it could still make for some interesting discussion.
This is how I envision each job to play. Feel free to add your own thoughts!
Paladin: the quintessential Tank, has the highest defenses amongst tanks thanks to its unique Block stat given by the shield. It has a relatively simple rotation and unique abilities to cover and heal allies, which makes them the ideal beginner tank with a pretty low skill floor and lots of recovery tools for yourself and allies. The skill ceiling is gradually raised with the introduction of a magical phase and 3 different stances (Shield, Sword and Magic) that boost defensive, physical and magical attacks respectively as well as add different effects to various skills, like added healing to Holy Sheltron in Sheild stance, added DoT to Goring Blade in Sword Stance or istant spells in Magic Stance. Players will have to juggle between stances as Magic Stance will put you into negative MP mode and you’ll lose almost all of your self healing when not in Shield Stance. Paladins can still be very useful in endgame raids both in progression thanks to their exclusive party wide mitigation and healing, as well as being the most mobile tank in Magic Stance, and with proper Stance dancing they can still dish out very respectable damage as they’re the only tank who can benefit from both magic and physical support abilities from allies.
Warrior: the king of “offense is the best defense”, it has no shields or pure heals, lowest defenses and fewer damage reduction abilities opting instead for more damage, Drain effects on his attacks, increased healing recieved and temporarily increasing his HP to be the highest amongst tanks. They have several crit-guaranteed abilities to maximize their self healing and damage done and can temporarily share their Inner Beast with all party members for an increased crit chance and drain. It has a higher floor than Paladin because of more incoming damage (you’ll see their HP go up and down a lot) and a buff+Beast Gauge to mantain but it’s still a great choice for beginner and the only tank to boost the party’s damage to take advantage of more expert players in endgame.
Dark Knight: the first of the 2 expert tanks with a higher skill floor, they specialize in shields and magic damage reduction. They have the least self healing of all tanks but the best shields and very powerful magic-focused mits. MP management is key as both shields and offensive abilities are tied to your MP, but you’ll be rewarded for optimal shield timing with refunded MPs to deal even more damage.