Comment by NayamAmarshe

Most of Sāṁkhya is theistic and came first. All purāṇas are sāṁkhya and theistic. Mahābhārata is theistic. Even Īśvara Krṣṇa never rejects īśvara in the kārikas. Only Gaudapada rejects it explicitly in his commentary. The sūtras, which came much later also don't reject īśvara, they just say it's not necessary (anivārya) to discuss, just like Darwinian Evolution, it's not necessary to presuppose there's a God but theists will still say that God sets it up in the first place.

To say something is not necessary doesn't entail that it's doesn't exist or that it's philosophically untenable.

Śankara does debate with atheistic Sāṁkhya so I'm not saying that it's not the case but it's a mistake to claim that Sāṁkhya is non-theistic because that's what some authors write when it's not the case. The majority of Sāṁkhya traditions were īśvara-vāda, theistic.