The SSD drives runs on the SATA bus, not on the PCIe lane. Someone already posted screenshot from Apple Profiler showing this.
And given the memory is soldered on (space savings) and SSD card (again for space savings) is quasi-proprietary, why WOULD you need to open the MBA???
And I have never heard of an Apple store charging for diagnostics. I know their service agreement at the Genius Bar mentions such a fee, but I've never seen it charged and I've been using the bar over the years for a lot of things.
And lastly, I don't know where the idea of low quality components entered anyone's mind. Apple's equipment isn't exotic, but it's certainly not low quality. They use Samsung Original memory in many of their portables, they source their CPUs from Intel, many of their hard drives are from Seagate, their SSDs come from Samsung, the touchpads come from Synaptics. I'm sorry, but the list of reliable manufacturers goes on. To say that an Apple uses low quality components is ridiculous. At least the casing is made from a single block of metal as opposed to plastic, and the keyboard letters are laser engraved instead of cheap melted-on plastic that rubs off over time, and that the trackpad coatings withstand years of abuse instead of wearing away and becoming smooth and frictioned... What in the world are YOU using??? Must be made from pixie dust and unicorn tears...