I have had no issues with my 300R connected to my PC. I have been using Drag-n-Drop without issue since I got the device in June. I do keep the device awake while transferring files, though. I had issues with older Android phones not keeping the connection open when the display turned off (Ca. 2010) so I have just gotten into the habit. I even use the front USB2.1/3.0 ports on my front tower panel with success. And no signs of my 3.5mm jack getting worse or loose. *knock on wood*
I will say that BT standards and protocols, like most things, are down to implementation. And lets be honest, car head units (especially factory) are nearly ancient in terms of hardware, so that may explain some of the issues people have. I use the AUX port in my 2017 Mazda and I am VERY happy with the quality (Line Out) of the audio through my factory sound system. I have played with BT using my phone (HTC 10) and found that the quality was significantly lacking. I also have a 64GB USB drive plugged in to one of the car's ports and the audio quality there, while better than BT, is also lacking. I don't buy cars without Aux Ports or Manual Transmissions because sometimes, simple just works better.
It is going to be a rough transition for ALL OF US when AUX finally dies out and we're left with poorly implemented BT and DAC systems everywhere. I don't see it getting any better, only worse.
~Ex