Prior to Update 11, this skill was called "Robust", and had no effect on your MaxStamina. The HealthRecovery was also reduced from 10/20/30% to 6/13/20%. Update 21 removed the HealthRecovery entirely and replaced it with UltimateGain when taking damage. This update also changed the level requirements from 5, 15, and 30 to 10, 20, and 40.
Robust: This passive ability has been renamed to "Stalwart." It now increases your Health Recovery by 6/13/20%, down from 10/20/30% and your Max Stamina by 2/4/6%.
Gain 6% Max Stamina and 20% Health Recovery → Increases your Max Stamina by 1500. When you take damage, gain 5 Ultimate. This effect can occur once every 10 seconds.