This place is funny. There are only two sides to this discussion. Fairy Tale vs. Reality. Pick your side. If you pick the latter, you should remember that people don't really want their dreams crushed and will ignore any evidence (read: repeated tests) while not providing any evidence to support the alternative view point.
Those same people will clean their brass, neck turn it, clean their primer pockets, de-burr flash holes, weigh powder charges, etc. all on the basis of someone else's repeated tests.
In case you aren't clear on which side is which. Jurassic park was a fairy tale. Gun powder is more like ping pong balls than stemware. A concrete truck is several orders of magnitude different than any tumbler reloaders would likely use. 200 hours is not 20 minutes.
OP should repost his question as, Can anyone provide evidence that tumbling loaded rounds to clean them is detrimental to their performance?