Yes. In lore, Guardians can actually use their abilities with much more flexibility and ferocity if necessary; the subclass system itself is there more out of identity rather than a strict limitation. Like Lasombra mentioned, it seems to be closer to a mana pool or form of stamina, and the limit of that varies between Guardians. Ability use mostly comes down mostly to imagination and experience/discipline. Some Guardians, such as the Vanguard, can repeatedly spam their supers if necessary. Other Guardians, Like Felwinter and Shaw Han, have used their Light to mimic that of other classes.