No unit is defined as a "tank." Every battle will have advantageous formations to survive longer.

Sometimes clones will protect your formation, other times immunity to status, dodge, super armor, etc....

Tanks you mean are superarmors? Other superarmor ninjas are not tank like sasuke rinnegan. I can tell if its tank , if its HP gain rate is above 2k. Its just me though.

Tanks are weirdly defined in this game because it really all comes down to power in the end. With enough power in your equips and other features, even a ninja like tayuya can take punishment for multiple rounds and still be fine. That said though, there are some defining features that could classify one as a tank. I'll name a few:

-Resistance and Defense scaling with every attack taken

- Passive skill that negates a single standard attack

- Dodge

- Low chance of being chased

- Regeneration before every action

- Ability to regenerate 60% and above of your health

- Super armor

- Immunity to debuffs

Those are some of the factors that you can build a team around on for certain situations to either outlast or completely nullify your opponents capabilities to maximize the amount of damage he can do. These are highly situational though. For instance, a team with full super armor will do great against those who rely on multiple chases to either do damage or apply control but will almost always be wiped out by heavy hitting standard attacks or nuke mysteries.