I don't think there's any need for them to re-look into this yet for balancing purposes until we're actually at that point in testing.
Stamina and Agility aren't necessarily the same thing, even if often used interchangeably, especially in typical MMO games.
Stamina would be more like your endurance. The more you have, the longer and further you can run or do something without rest.
Agility would be more like your speed, being nimble, quick dodging and manoeuvrability.
Take a sprinter for example - most of the time their agility is high, but they may only be able to sprint those short bursts before slowing down or taking a break. An endurance runner on the other hand has less agility, but can run for much longer than a sprinter, in one go, without taking as many breaks.