I'm not sure how common this view is though, since TUR was a shengtongpa.
The three samadhis are clearly taught in the root Mahayoga tantra - the Guhyagarbha - and in every commentary I'v every encountered. However, as I mentioned in a previous post, there is a provisional, conceptual way to approach it until one has knowledge of the natural state. But, of course, it is obviously going to be more authentic a practice for one who has clear recognition of rigpa. I think that's what is being said.
Pero wrote:TUR himself says that you can't achieve enlightenment through it alone, so it is a "lie".
In general the impression I got from reading his books is that TUR is teaching Dzogchen to Tantric practitioners. That's why he says things like the deity develops from the natural state. But you forget that not everyone of us has the capacity to understand the natural state. IMO you can practice deity transformation without understanding it. If it would not be so there wouldn't be three inner tantras, there'd be only one.
I think when he says that you can't achieve enlightenment through development stage alone, that means that the development stage must always be in union with the completion stage, i.e. one must at the very least maintain the correct conceptual view of emptiness during the generation stage. All Nyingma generation stage sadhanas begin by (sometimes cryptically in shorthand) referencing the three samadhis. Also, the three inner tantras in Nyingma are all very connected. It's not as if Mahayoga and Dzogchen are so separate. For instance, Dzogchen is taught in at least one chapter of the Guhyagarbha. Also, an important Dzogchen tantra (whose name escapes me but which I could look up at some point) states that Mahayoga is the ground, Anuyoga is the path, and Dzogchen is the fruition. Also, since the 4th empowerment is present in all inner tantric empowerments and in Nyingma it is
the direct introduction to rigpa (and in some Nyingma empowerments it is more lengthy and elaborate and quite obviously pure Dzogchen), a recipient has received the transmission to enable him/her to recognize rigpa. For a time, though, one is naturally going to have to approach the three samadhis from a conceptual, dialectic type approach like I mentioned in my last post.