Cartuja

High HP + HP Scaling

Cartuja has some of the highest base HP in the game (plus a +HP% Imprint Concentration) and very respectable Def. On top of that, he has HP scaling on all of his damage, which further incentivizes him to gear himself like a brick wall.

Spammable Defense Break

Since Cartuja causes Defense Break with his S1, he can always use it whenever you need it (as long as he's not Stunned or otherwise disabled, anyway). His infliction rate isn't the highest, but being able to use it as much as you want can be helpful, especially in long PvE fights like Banshee 11.

Self-CR-Push When Attacked

Anytime Cartuja gets attacked, he gains Combat Readiness. This helps offset his low base Speed and also helps him burn down the long cooldown on his S3 more quickly. He also gains more CR when he's low on Health, helping him get a crucial turn to use his S3 when he needs it.

Self-Sufficient S3

Cartuja's S3, Predatory Roar, is his claim to fame. It causes Attack Break to all enemies, grants Defense Up to Cartuja, deals more damage when Cartuja is low on health, and heals Cartuja in the bargain (as if the rest wasn't enough). If Cartuja pulls this move off, you can bet it's going to take at least one more turn to kill him, if not several more.

Free Connection Hero

As a free Connection Hero, Cartuja is easy for any player to recruit (although the price is admittedly steep). Especially for players who really need a good tank for Banshee, Cartuja is an easy, convenient option.

Low Damage

Despite the HP scaling on his attacks, Cartuja's damage tends to be unimpressive. The scaling isn't quite high enough for him to be dangerous, and his base Atk is pretty low, which holds him back even more.

Unreliable Defense Break

While Cartuja's Defense Break is spammable, it's not very consistent, capping at a 50% chance after Skill Enhancement. This is a problem because Defense Break is the most threatening thing Cartuja can do to the enemy team, so if his Defense Break isn't landing, Cartuja isn't contributing much.

Hard to Build

Cartuja is extremely stat-starved. He wants HP to stay alive, but he also wants Def because he wants to take a lot of hits for his passive. He needs Effectiveness for his ailments and Effect Resistance to avoid being disabled, and he even needs Spd because his passive relies on him getting attacked and he's very slow when it doesn't trigger. This makes building him quite difficult.

Lacks Impact; Easily Countered

This is the major problem with Cartuja: he can't really influence the course of battle on his own. He's great at staying alive, but since he's very bad at killing things, he's not going to pull out a miraculous one-man win if the rest of your team dies. And since he lacks any kind of Provoke and isn't a Knight who can equip Elbris Ritual Sword or Aurius, he isn't able to draw aggro from the rest of your team. Cartuja is easily counterplayed: simply pick off his allies rather than attacking him, and there isn't much he can do about it.