What is really good about paladin is they can heal themselves and others indefinitely. This makes a lot of content, especially dungeons soloable. Where other tanks might have to play really well to solo it and hold onto every drop of health they can retain, paladins can just yawn and cast their powerful heal over and over. The benefit is that if your healer cannot heal for any reason such as a disconnect, death or lack of gear, you can takeover the healing and make it work. You can also heal the healer when they are about to die, such as when they are encased in ice.

It always has a tidy 60 second rotation with plenty of variety, like a dot, powerful combos, a buffed phase and a magic phase. The magic is really nice, although I personally enjoyed it more in Stormblood because later on the cast time is removed. It's half melee half caster.

You get other fun ways to protect others, like Cover to take all damage for someone and Passage of Arms which looks really cool in phase transitions.

Paladins used to be most famous for Hallowed Ground, which makes them completely invincible for 10 seconds, but now other tanks have similar ones and a lot of other things make up paladin identity now.