To be clear, I am referring to only the report made by Kron here.
As you said, there is a lack of proof in his report. But that's not the reason given by two of the staff members for dismissing it. I'd be satisfied if that was it, even though for a bug like this, proof is less important. Why? Because the purpose of providing proof is to show that the author put at-least some effort into making the bug report. Even if proof is given, the Devs would've to check it themselves thoroughly since there's always the chance the author can make a mistake, just like you said. But here, the bug in question is not some silly visual bug that very few people care about. This one is important enough to warrant attention from Devs even without proof. And enough people are talking about it, so this isn't someone randomly creating reports of big bugs to flood the bugtracker.
How long did the report for Stampede, the most-voted ( at that time) report stay in bug tracker without getting fixed, even after numbers were thrown at it from a multitude of angles? What about Deterrence bug in Wotlk? And so many more with proof in the bugtracker have gone too long without fixes. Clearly, providing proof can't be held as the sole reason for a bug not getting fixed, or atleast taken into consideration.
Still, I'd be satisfied. But again, this is not what caused the report's dismissal.
Let's say someone is trying to find proof, taking into consideration what you and the staff have said. How would they go about it? You've laid out the step by step instructions and I truly appreciate that effort. But, which trinket should be tested first? Will the person have to just test the one or two trinkets he can get and then extrapolate to assume the other trinkets are/are not bugged as well? Players who've been here for a while would know that when it comes to bugs here, such assumptions are weak footed and thus counter-productive to the process of proofing. Only a thorough testing would be acceptable.
So,would he/she have to test out each and every other gear and trinket, make reports (if need be) for them separately?
For this, that person would need atleast a few classes at level 90, and all the gear and trinkets worth thousands of VP and whatnot. Thus, the players eligible to provide proof would be those who have put in a very large amount of time and effort in MoP here to gear out many characters in PvE, or donated for a considerable amount. Another option is to ask friends with high end PvE gear and the proper classes. That's hundreds of gear and trinkets to test. Also, all end PvE content isn't even fully scripted here, afaik.
Clearly, this is way too much effort for a player to go into making a proof that serves such a needless purpose. If this testing is done by a GM, it would be much, much easier. Given that they would need to do it by themselves anyway, even if proof is in report, why shouldn't the GMs try it first?
If the bug in question had been about an ability, like Stampede, players could provide proof with effort. In that case, your answer would've been perfect.
Looking at all this, and then checking the report made by MysticElegy, just shows that it was an attempt of desperation which I perfectly understand. His report is ****ty, sure, but his attempt at it is definitely understandable given the reason for dismissal of Kron's report. As for his report, if I was Q&A, I would delete it, but no ban. :)