This is a misleading assertion born from an inadequate understanding of pUrvamImAMsA. I would like to state that I point this out not to discourage, but to highlight the intricate nature of this highly misunderstood Astika school of thought, which itself has historically diversified into three prominent sub-schools. The very svabhAva of pUrvamImAMsA makes it inherently hostile, very much so, to its adopting by members or groups outside the Astika fold. Without accepting the philosophical, analytical, and exegetical underpinnings of the apaurusheyatva doctrine, it would fail to be pUrvamImAMsA. The jaiminisUtra, shlokavArttika (esp. the codanAsUtra portion), and even Dharmakirti's pramANavArttika explain this characteristic of pUrvamImAMsA. Regarding other Hindu philosophical systems, I'm sure some compromises can be made to make their accommodation more pleasant and well transitioned.
If Indo-Pagan implies folkish variations, I would very much be an Indo-Pagan. In addition, being the only staunch Hindu polytheist, with hard inclinations, here on RF automatically makes me very much pagan to even other Hindus with pantheistic, monist, dualist, etc., bends. On the other hand, if Indo-Pagan implies amalgamatious or syncretic expressions of Europagans, African-pagans, Japanese folk-variants, Chinese folk-variants, and the rest of the whole shebang, coming together with village Hinduism, I feel it to be only natural that the worshipers of numerous gods and goddesses, each glorious and contextually important, find commonality and brotherhood amongst one another. In fact, I find more in common with, say, Japanese folk-variants than I do with orthodox Vaishnava-s, not to mention how Hindu gods have a unique, and "in a Japanese way", so to speak, presence in Japan.
However, what I, as a Hindu, would find concerning is the mis-attributing and/or misappropriation of Hindu, as well as other non-Hindu but Dharmic figureheads, concepts, and objects of prominence, by pagan circles which, as per my observations, have had the tendency to involve back-preaching (i.e., Hindus are practicing their religion incorrectly; Hindus should go back to the Vedas; the Vedas belong to us not modern-day Hindus, Hinduism is not vaidika; etc.). Where this tendency to articulate "true _______" came from, I'll never really know. However, the fact that it occurs is concerning, nonetheless. It isn't the job of any pagan practitioner, including Hindu polytheists, to urge that one is practicing their faith, which is highly socio-cultural in nature rather than theological, doctrinal, credal, and textualistic, in an incorrect manner in the hopes to return it to a construction ultimately imaginary and prone to conjecture. This isn't how most non-Abrahamic faiths operate, nor have operated historically. Socio-cultural realities and that of the bahudeva (Sanskrit for "many-gods") have often gone hand-in-hand. If I was in another country that has a sizable population practicing their faith in their own cultural manner, it would be disastrous, and a grave affront, for me to complain that they me be expressing their own socio-cultural realities and divine acknowledgement improperly. That is their own expression; as a guest, I would be highly honored to just even be invited and observe how my pagan comrades of that locality operate or function. Likewise, if I find myself in Norway, Sweden, China, Iceland, and/or Japan, and other related countries.
Paganism, in general, has functioned well on pluralist grounds with the automatic understanding that worshipers of many gods and goddesses have their own way of doing things. If I went back in time and found myself in Ancient Greece, it would do me no harm to offer acknowledge to the Hellenic gods under the guidance and assistance of a native practitioner. And if both the ancient Greek and the ancient Indian were to come together socio-politically, we would notice the happening of the same things that occurred in Gandhara: the incorporation of both Hellenic and Indic deities through amalgamatious expressions. Not really theological compromises, but rather socio-cultural compromises, and understandably and rightly so. As I have always said, I long to see the European resurgence of the intricate and unique pagan expressions regarding their ancestral gods and goddesses and of their folk-variants---I should interject by adding that I long to see similar resurgence elsewhere in the world, and hopefully in other countries that have had that history. Glorious Iceland has taken a wonderful step in acknowledging, quite outright, her pagan past through the recent creation of a temple. I hope other countries with a similar history follow suit, though naturally---and by naturally, I mean through an honest, internal drive to reconnect.
Aryans this and Aryans that. Aryan, Aryan, and Aryan. The problem with Aup-dada's involvement in such threads, a recalcitrance that occurs with Colonial-derived veracity, is that it indirectly, whether he means to or not, monopolizes the understanding of ancient Indian tribes and parcels about a view that is ultimately in a constant state of refinement, not to mention that the mere treating of such a term purely on racial and ethnic grounds, as he does, has long been discontinued. Furthermore, such participation is rather discouraging. While meaning well, it comes along Indologically, not Hinduaically. It would have been more beneficial if other, and more, Hindus participated in this thread; their lack in presence, however, illustrates how the OP's subject matter is something rarely ventured upon, unfortunately. And it's unfortunate because some of the greatest camaraderie the Hindu can find, apart from other Dharmics, is amongst pagans.
Well, it's most certainly true, as per orthodoxical, indigenous, and Indological narratives, that the upaniSad-s are part of shruti. They, along with their sectarian and/or sub-schools of thought commentaries, constitute the j~NAnakANDa of that which is shruti-derived; the Veda-s, along with their associated brAhmaNa-s, dharmasUtra-s, gRhyasUtra-s, shrautasUtra-s, etc., constitute the karmakANDa. In a simpler, as well as historical, usage, that which is declared Veda is well beyond just the Rg, sAma, and yajur (as well as atharva), incorporating various upaniSad-s in the process. Known as rahasyavid, they have always played a prominent role and today act as the theological underpinnings of much of modern day Hindu thought, the latter of which has highly been influenced by Vedantic understandings.
However, in regards to the "historical Vedic religion", I would like to express a few and brief thoughts on the matter. Such a classification of "Brahmanism", another classification which in and of itself is misleading, is conjecture at best, and born from the assumption that it was a widespread, mainstream occurrence once upon a time. If anything, the "historical Vedic religion" has never been mainstream, and understandably so. And it wasn't even a religion, per say. It was confined to a select few who were very much exclusively inclined. They could hardly be used to classify the karmakANDa as constituting an ancient Indian religion of some sort. Even the warriors, kings, and laypersons that sponsored their services in order to conduct contextually-relevant rituals had their own folkish inclinations. The "historical Vedic religion" is ultimately a construction, by observers far removed from both cultural and religious ties to the subcontinent, pedestaled to unnecessary heights, largely based on etymological assumptions, some of which do have merit, I'll concede, in order to understand both Indio-Iranian and early Indic society. While the gods such societies may have worshiped may have "Vedic" origins, the construction does very little in explaining non-Brahmanic realities outside both Astika (orthodox) and nAstika (heterodox) socio-political confinements.