Do you consider loose buttons and dead pixels to be "fine"?
Yes, a dead pixel or two are fine. In fact, 10 dead pixels on a iPhone 6+ screen would only be 0.00048% bad pixels. Most people wouldnt even notice it.
Face it, you just got lucky. I have a loose mute switch, but as my other buttons are firm and my screen perfect I didn't tempt fate by exchanging my 6+.
A loose mute switch isn't a defect unless it actually affects the functionality of the device. The issue I have is that people post these "problems" that aren't actually problems.
Let's face it though, the most expensive production smartphone in the world should have perfect condition hardware out of the box. If it cost $100 outright then I might be more forgiving.
Again, nothing is perfect. A certain number of minor defects is always going to be acceptable, regardless of the price of the device you're buying.