You may be on to something, for me, as soon as I moved to using the TP-Link USB nano WiFi adapter, all the problems vanished. The one issue you mention that when you try to wake up the SP3 and it took forever to respond, is also solved by using an USB wifi
adapter. Basically if you disable the onboard wifi card and use other hardware for it, everything works beautifully!!! Like it should be.
That is why I can live with the SP3 now without worries, believe it or not, the connected standby does work with the USB adapter as well. All this is at the expense of some battery life of course, but it is not awful.
So, yes, I think it is a hardware issue plus more software as well. Maybe Microsoft should bundle in the USB Wi-Fi adapters :)
I do think it is crazy that they are not even acknowledging that there is a problem and users have to resort to ask the community for answers. This is supposed to be a premium device and I personally feel like I just bought something on eBay because I have
no support of any kind.
Not many units may be flying off the shelf, otherwise they would have a major press issue as well.