Is Siddhartha posing a counterpoint to the Hindu creation belief of the abstract one god gazing upon himself by tuning the mind to subjective perception of the material universe?

I believe that to a certain extent he does, it would be necessary to see what nature he gives to the ideas to know if he places them in the same rank as the sensations, or if he gives a higher step as Plato does, however, both forms of perception are still inherent to the subject and therefore, following Buddhism, they must be transcended.

As for the material world, he refers to the All talking about the sensible and the intelligible, therefore, it is not about denying something beyond this, which could very well exist, but it shows the impossibility of perceiving something beyond this.

Furthermore, when he talks about ideas he may already be referring to something alien to matter, although again, it would be necessary to see what nature he gives to ideas.

And yes, I believe that both karma and caste Buddhism does not deny them, nor does it deny intellection and sensation, but it seeks to transcend them.