My thought on this is every guardian has the potential to master more than one of the elements, solar, void or arc. However, most will specialize in one in particular. They will favor it and almost use it exclusively. Eg. Cayde used almost always solar, but he kind of talks like he probably has used arc before. Zavala so far has done arc and void, same with Ikora. Just because we havent seen them use all three doesnt mean they can't.
I would argue those that get chosen for the vanguard are probably able to use all three. Does it mean they do, nope not at all.
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Zavala cannot use hammers, he hated the sun breakers But that’s the exception, I’m sure Ikora can use them all, and Cayde can probably use arc, and maybe void