I don't have any disagreement with most of what you say here (as I'm not an expert on this), but:
There is considered to be a subduction zone beneath part of the Carpathians in Romania. I don't work on the area, but read a couple of papers on it-so I'm not sure of the following: it is likely to be the final stages of subduction of some sea that used to be there (the Alpine belt formed that way). There is something called "slab rollback"-the more dense slab is sinking down rather than sliding straight down along its dip....
I don't know, but think it likely that the same sort of thing could be happening beneath the Hindu Kush (an old slab still sinking). There has been some papers on a high-velocity anomaly beneath the western Transverse Ranges of California: that all the convergence there has started a downgoing "drip"....

Because of temperature-pressure conditions that you discuss, I believe that most deep earthquakes are considered to occur within the stronger slab. In contrast, the damaging subduction earthquakes occur at shallower depths at the interface between the slab and the overriding continental crust.... Chris