I think it is wise to keep them separate as understanding proceeds in quite different manners. For some [including me] one system may complement the other [with the peril to be unsuccessful in both], but that does not justify unnecessary simplification and forced syncretism.
I think even a cursory reading of my posts on this matter here and elsewhere would not lend justification or even the idea of "simplifying" or mandating syncretism.
The very point of syncretism here is that these traditions are mutually revealing thru illustrative, complementary
differences, while sharing an ultimately identical view or, perhaps better, viewless position.
Nonetheless, a syncretism between tantric traditions, whether internally - as in Buddhism's Rime - or between slightly more disparate traditions - is actually reflective of their root sameness.
You brought up the concept of 'samaya' which, though burdened with different meanings and other sandalwoods in the Hindu and Buddhist traditions, is a core concept in the tantras.
I suggest we take a mutual initiative to explore the samenesses and differences between Hindu & Budhist tantra.
I have an unfinished article for this DIR that I promised SageTree almost 3 months ago that is still collecting dusk on my harddrive, perhaps this will serve as part of the needed impetus to complete it.
In the brief scope of this post, the one thing I consider most valuable in terms of my own practice is the (more or less) reversal of esoteric gender roles. In the mainstream Hindu tantra, the basic idea is that the Male principle is consciousness, and the Female principle is Power or Display, sublated by an underlying unity [shiva shakti samarasa]. This is probably infuenced by early upanishad-era ideas about Brahman and Maya, and corresponding Samkhya/Yoga ideas Purusha & Prakriti coming into currency - and therefore exchange.
By contrast, having placed their anchor well past the range of hedged dualities one finds in the range of Hindu tantric traditions by means of the madhyamaka, the Vajrayanists assign the radiant void, the black womb of the tathagatas as Wisdom/Awareness, and the male principle instead as Upaya & its motivation, mahakaruna <and its nondual cognate, bodhichitta>.
Entertaining either view variously, or both at the same time, I have found far more fruitful, and in accordance with the principles of samaya and samarasa, like the nectar gained from churning the poison of identification, and have come to the conclusion that it's the doctrine-by-implication of both systems.
So, in discussing Hindu & Buddhist tantra, and the meaning of tantra itself, the underlying gnostic praxis that is independent of either culture or religious dressings, I I feel we should set the stage by discussing the following, perhaps in this order:
1. Kapalikas, Pasupatas & the origin of the twinned Siddha & Yogini lineages
2. The Siddha & Yogini streams metamorphosizing variously into Kaula, Natha & Sahaja approaches (all closely related) as well as the Vajrayana (with analogues to the other 3, especially Sahaja).
3. Individual luminaries shared by both, including both historical figures
and deities, along with their iconographies, ars memoria & symbolic syntax. Historical figures would number among the 84 Mahasiddhas, I'd like to pick out Saraha for discussion in particular.
4. Later sectarian developments and clashes, attempts of one system to subvert or convert others, and how this is reflected thru deity yoga systems & the mythologies of subjugation.