Is Buddhism a reduced version of Samkhya philosophy?

According to the wikipedia page on Samkhya:

The earliest surviving authoritative text on classical Samkhya philosophy is the Samkhya Karika (c. 200 CE or 350–450 CE) of Īśvarakṛṣṇa. There were probably other texts in early centuries CE, however none of them are available today. Iśvarakṛṣṇa in his Kārikā describes a succession of the disciples from Kapila, through Āsuri and Pañcaśikha to himself.

So, Samkhya philosophy as known today, came almost 700 years after the Buddha (c. 563-483 BCE) based on the date of Samkhya Karika. But as stated above, it is attributed by Iśvarakṛṣṇa to Sage Kapila, who obviously predated the Buddha.

It is possible that the Samkhya Karika had experienced influence from Buddhism.

What about Alara Kalama?

Apparently, the only source stating Alara Kalama as following Samkhya is the Buddhacarita, composed in the second century CE by Aśvaghoṣa. This too was written at least 500 years after the Buddha.

There is no mention of the Samkhya philosophy by name in the Pali Canon. The Pali Canon also never explicitly attributed any teachings to Sage Kapila. The only mention of Kapila is in the Jataka Tales, dated at least a century after the Buddha.

In any case, whatever doctrine or teachings that was taught by Alara Kalama to the Buddha, did not bring him enlightenment, as we see in MN 26:

"In this way did Alara Kalama, my teacher, place me, his pupil, on the same level with himself and pay me great honor. But the thought occurred to me, 'This Dhamma leads not to disenchantment, to dispassion, to cessation, to stilling, to direct knowledge, to Awakening, nor to Unbinding, but only to reappearance in the dimension of nothingness.' So, dissatisfied with that Dhamma, I left.

So, the question is - did the Buddha copy and reduce Samkhya, or did the Samkhya Karika copy the teachings of the Buddha and tried to reconcile Buddhism with the teachings of the Vedas and the Upanishads?

Based on the dates of the writings, I would say the latter is more likely. So, you've got it in reverse.

But did the Buddha copy Sage Kapila? Well, this is impossible to say, because we don't have any authenticated pre-Buddhist writings of Sage Kapila remaining, in which he taught Samkhya.

Based on the following statements from the Samkhya Karika, the definition of Spirit (Purusha) is in violation of sabbe dhamma anatta (all phenomena is not self). There is no single Self or Spirit that is the pure witness or controller in Buddhism.

The Spirit exists because (a) the aggregate is for another's sake; (b) of the absence of three guṇas and other properties; (c) there must be some controller; (d) there must be some experiencer; and (e) of the tendency of activities towards final beatitude. - Samkhya Karika 17

The multiplicity of the Spirit is verily established (1) from the individual allotment of birth, death and the instruments, (2) from the non-simultaneity of activities, and (3) from the diverse modifications due to the three guṇas. - Samkhya Karika 18

And from that contrast it is established that the Spirit is the pure witness. He is solitary, neutral, spectator, and non-agent. - Samkhya Karika 19

Last time I had the pleasure of speaking with the Buddha, he said that most of what he teaches he indeed had learned from Alara, but only after having completely realized and verified it in his own direct experience.

Before he realized it in his own experience, he could only "pay the lip-service" to the teaching - he could say the right words from memory - but he hasn't connected it with his own reality yet.

Words are cheap if you don't really know the truth.

Alara heard all the right words from his teacher and realized most of them in practice but did not attain Final Enlightenment and Liberation. The Buddha learned the theory that was passed from the previous Buddhas, an echo of previous Realizations - some parts still clear and some corrupted or lost. He got the gist and followed the tracks until he got to "the lost city".

The Dharma is a teaching about reality and about mind. It's like science it describes the laws of nature (just the different laws). It's no wonder that it has been rediscovered in some generations, then passed down, then lost, then rediscovered again. It's not an invention of the Buddha.

Why is it surprising that he learned much of it from his teacher and got the rest by himself?