I think your theory is very plausible. Valve always goes late when it comes to updating its hardware databases, and so it's possible that part of the new Turing cards aren't properly identified. And when it comes to AMD... well, I was going to say what for the first gen of Navi cards because they're capable of mixing the new ones with them but, since they're down, they haven't done it (yet).
We'll see if they've updated it next month.
Please excuse my bad English.
Currently gaming on a PC with an i5-4670k@stock (for now), 16Gb RAM 1600 MHz and a GTX 1070
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