This is the junk passive of ESO, and it honestly needs to completely change. First let's look at the 3 races that have this passive: Khajiit, Orc, and Nord
Both the Orcs and the Nords are known to be natural warriors (heck the Nords were the only ones that could put the elves in their place), and the Khajiits have been more known for their stealthiness. In ESO both of these playstyles are primarily stamina focused, and because of it I think Robust should give +6% max stamina, and +6% stamina recovery in combat. By doing this you will add the much needed resource management these races desire, and should have.