Recently I replayed the part of the Temple of Mythal where we first encounter the Wardens and all the dialogue definitely says they are mind controlled. The Inquisitor says they are enslaved and Cassandra says "If they are forced to obey him, death will be a mercy."
We know that Corypheus can influence the Wardens to free him when he's unconscious and that he can mentally prevent them from killing him when he's awake but confused. That is something both a codex entry in Legacy and Varric's comments in Inquisition both attest to. It's not even a stretch at all to think now that he's awake and more lucid he can control Wardens even more. I really don't see how anything in either game even hints at any other possible conclusion.
Neither characters line is proof of anything. The Inquisitor absolutely does not know what Corypheus can do. Neither does Cassandra. It is purely speculation. Again: even if we accept they are mind controlled there is nothing to justify the inference it is from some innate power of Corypheus.
It is an incredible stretch to go from "can influence" to "can dominate". To use an example: the fact that humans can outrun a tortoise is not proof they can outrun a cheetah.
The only instance of mind control we see is demon binding - done by a Tevinter human mages - and blood magic.