Stamina arent useless at all… Monk Double punch uses stamina instead of Sp which is very usefull and it saves a lot of sp and there are classes that rely skill cost with Stamina instead of Sp…
From blog.
Q) Why is Stamina system in the game? What’s its use?
A) During the beginning phase in the game, it is used to limit your character’s movement speed, but as your character’s rank increases, it may also influence your character’s skills depending on your character’s class attributes.
For example, there’s a skill called Shield Charge used by Rodelero which you will use while moving. The skills like this will get influenced by the amount of Stamina you have.
Stamina will also be consumed when you are controlling your companions so eventually Stamina will be another parameter that you will have to manage in the game.