Mara is something else, she used to be a Human who fled from the collapse, but something happened in the collision of light and dark , to make her paracausal(supernatural) , and she is a being of immense power, she has her own throne world , and created an entire new race from the survivors of the exodus ships fleeing the pyramids, The Awoken Mara doesn't need the light, she has a throne world, and is a diety herself, if we lost the Traveler and The Darkess powers, she could give us powers , she essentially empowered us in Season of Defiance to save hostages, and break the shadow legion Oh, and don't listen to the clown that is obsessed with there being a 10 year secret plan to turn her evil , she is firmly on our side

I’d say all three combined

If bungie went that route I feel that they'd make her a titan as a surprise twist. Lore wise if I remember correctly technically a light barer can learn all three disciplines but it's meant to be really hard and rare.