It is reasonable to assume that DNA under JonBenet's fingernails could easily self-transfer to her long johns and panties. The same can be said for DNA from under Patsy, John or Burke's fingernails. There are innumerable ways the four Ramseys, or anyone, could pick up artifact DNA and transfer it.
It is reasonable to assume the garment could have been mishandled since in 1996 maintaining a chain of custody was a priority but handling evidence to maintain pristine DNA evidence was not understood like it is today.
The Codis sample had to be amplified before CODIS would accept it. It was not a full, native profile and it reportedly was degraded.
It is unreasonable to decide guilt or innocence on such indirect evidence and even more so to decide guilt or innocence only on one piece of evidence, especially that which is questionable. Saying the TDNA and the minute mixed sample in the panty belong to the killer is ludicrous without other direct evidence that goes along with those samples.