The Samkhya/Yoga and Vedanta views are quite different. The situation is
complicated by the fact that Vedanta has more or less completely absorbed
Samkhya/Yoga notions and terminology.
This is the Samkhya view:
Purush --- Prakriti
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sattva rajas tamas
The advaita view is more like this:
Purush
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Prakrti
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sattva rajas tamas
In Samkhya/Yoga the observer is completely detached as you say. Hence
it is dualistic. In Advaita Vedanta the observer at one livel *is* the
observed. The relationship is normally masked by the delusion of Maya.
but can be discerned through contemplation.
But like I said if people know terms such as Purush, Prakrti etc. at all
nowadays it is through a Vedantic filter. I don't think the
Yogasutrabhashya (actually a tika on the Vyasabhashya) is genuine but the
fact someone even tried to pass it off as genuine shows how entangled the
Samkhya/Yoga and Advaita traditions have become over the centuries.
Whatever you think, that you will be.
If you think yourselves weak,weak you will be;
if you think yourselves strong,strong you will be
—Swami Vivekananda