Some elements can definitely reasonably do a wider array of maneuvers (compare fire to air, earth or spirit) but for the most part, each element attacks and blocks in a fairly similar manner (mechanically). You don't need ALL the elements to do whatever you need to do.
It doesn't seem to me that someone who has Air, Fire and Spirit (But not water or earth) is weaker than someone with Air, Water and Metal (but not fire, wood or spirit) or someone with Ice, Entropy and Light (but not Cloud, Darkness, Wood, Earth, Fire, Law, Water, Spirit and Beast).
As long as whatever chosen elements from the system you believe in give you a wide enough array of reasonable effects for you to play your character effectively, it doesn't matter how many other elements you think are out there.
In the books, there are various types of evocation that people and boogin's throw out. Stylistically/mechanically, some work better as sponsored magic, but some could easily be reskinned as elements.