From my admittedly little time on the site, I don't think I've seen any noteworthy threads come from the Proving Grounds in the last year or so. If anything the opposite is true - most of the high volume threads I've seen lately are made in Multimedia or General Discusssion to sidestep PG, with little or no information added to the OP at first. ProJared and the Weeb Wars shit come to mind - they're high traffic and have very dedicated readers, but I don't think for a second most of what those threads started out with would have made it out of PG in time for them to take off.
I have a small anecdote that while irrelevant to most other users experiences, I think it highlights my problems with PG. My only attempt at trying to write an OP for Proving Grounds was making a Mumkey OP before any of the big drama hit. I had a chronology of his fuck-ups and friends written, but it didn't have any doxes and it seemed poorly written so I just shitcanned it. A week or two later someone made a thread on him in Multimedia circumventing PG and only had an embedded video and only wrote something along the lines of "this is Mumkey, here's a video about him". It soured me on the idea of the Proving Grounds because even with a very blah start, the thread and OP turned out great; almost certainly better than mine would have been because it gave other users a chance to add their own understanding of events to the discussion. If better and more popular threads can be made without PG's restrictions, why bother with it? I say get rid of Proving Grounds, and if it floods other boards with low quality shit too much just reinstate it as is.