I think some core points are being missed:
- polytheism is not mutually exclusive with the idea of a single supreme being.
- Nowhere, different deities being described as forms of the “One” is intended to be mutually exclusive with those deities having separate existences.
Often, the allusion to trimUrtis or all devas being forms of the “single supreme deity” occurs in the sense of the Self (often explicitly identified with the single supreme deity) manifesting as all. This account doesn’t negate our individualities at all. There is, simultaneously a continuity & abruptness between the single supreme god & other devas.
The continuity is reflected through such usages as “devottama” or “devadeva”, when referring to the former & “anyadeva” when referring to the latter. These usages reflect that the single supreme being was essentially seen as being part of the same class as the anyadevas, or else the term wouldn’t make sense at all. This is the continuity of being between the devottama & anyadevas.
Non-monolatrous henotheisms would have the worship of many deities but accord only one deity the highest position in both doctrine & worship. Monolatry accords worship (latria) to only one (mono) deity.
Hindu case
The abruptness comes from the devottama being Ishvara. But this doesn’t contradict the account that Hindu dharma is polytheistic. There is similarity of genus but utter dissimilarity in terms of supremacy since only one being can be supreme.
Source: TW
Too often, many modern-day interlocutors of traditions, unfamiliar with what the terms mean, are also too quick to denounce the label of polytheism as well. This only feeds the inferiority complex that Hindus have regarding polytheism and make them opt for some version of monotheism, no matter how vacuous it is.
Saiddhāntikas & Mādhvas have an important role here because both systems have a rich polytheist ritual praxis (worship in accordance with tāratamya) even if we accord Paratva to only one. Even Śrī-Vaișņavas, despite their strong emphasis on ekāntībhāva, have to honour Nityasūrīs and Pāñcarātrika Āvaraņa/Parivāra devatas.
Notwithstanding all of this, all of these groups + Advaitī Smārtas have to perform vaidika nitya/naimittika karmas, which are premised on the individuality of Devas, since each Deva is the rightful recipient of its own proper honors/offerings.
It is important to emphasize the multiplicity of gods and that we have real obligations towards real beings. They are not just some metaphors.