The point is that you already admitted that wasn't true. That same protein undoubtedly exists in countless nylon-free environments around the world today. It is neither new nor novel.
"The mutations for producing an enzyme capable of digesting nylon might well have existed thousands or hundreds of thousands of times in the past for brief moments; but there was no survival advantage to having it and so it was lost through natural selection."
Not only in the past, but in the present in nylon-free environments. This means that it is neither new nor novel and your claim is destroyed.
The population did not have the enzyme to digest nylon until it mutated the gene for an esterase enzyme, then a NEW protein was made that conferred a NOVEL ability (the ability to digest nylon being predicated upon the existence of nylon).
My claim has not been destroyed. My claim is supported. My claim being that living systems are capable of changing such that new proteins come about and novel applications can be found for them.
How blind must one be to characterize this change as devolution?