As a very experienced FAA test pilot said many, many years ago - "when you get an aircraft that has a type certificate, you can be assured that you're getting something that is minimum specification".
What that means is that it is at least, but probably not much more than minimum specification.
If you were looking at a non-certified aircraft and knew a lot about structures, systems, flying qualities, reliability, etc. you might be able to get a machine that far exceeded specifications (and many of the really good kit built fixed wing machines are good examples of that), but if you didn't really know a lot, you could end up with something that was well below the minimum necessary for safety (in any one or all of a number of areas) and not know it till it was too late.
One only need look at the accident rate for home-built aircraft to realize the truth about this problem. Balancing that is that most of the real innovation in aviation today is coming from the experimental side, not the established manufacturers. They can't afford a major mistake.