The six darshanas are usually listed as pairs, and the pairing is not decorative: Nyaya supplied the logic and epistemology, Vaisheshika the physics of atoms and categories, Samkhya the dualism of consciousness and nature that Yoga then made practicable, Mimamsa the analysis of ritual and language, Vedanta the interpretation of the Upanishads. Samkhya as a system does not require a God and says so. Mimamsa is concerned with the correct performance of sacrifice and is nearly indifferent to liberation. That two schools this far apart are both orthodox tells you what orthodoxy meant here: it was about the authority of the Veda, not about doctrine. The genre of Indian philosophical writing reflects this — a text states the opponent's position at full strength, then answers it, and the opponents are quoted so scrupulously that some lost schools are known to us only through the refutations of their enemies. Vedanta swallowed most of the others in practice after the twelfth century, which is why an educated Hindu today is far likelier to have heard of Advaita than of Nyaya.