You have to look at it from FiiO's POV - they are only in the DAP market for 2 years or so, so they are only just learning to code their own firmware since they came into the market. Whatever history Apple, Google and Microsoft have is not going to help them much since they are wring their own firmware from the ground up with a small team of in house software engineer and a fairly limited budget. To say there is not much difference between every DAP is more or less naive to the situation. If coding is so easy, we won't have MacOS and Windows keep needing bugfix when both have been in the market for ages.
totally agreed with what u said, every company has their limitation, sometimes times are required to become better, (eg, even iphone 5s has problem of fingerprint sensor got cracked), no offense but everything has its limitation, it's good enough to reflect it to the company, no need to keep on mention about it