From what I can tell, there are actually very few Rock-types in OU or even BL:
OU: Tyranitar
BL: Aerodactyl, Regirock, Rhyperior, Rampardos
That's 5 out of 20 rock-type pokemon. So, the vast majority of rock-type damage being dealt in the typical OU match is from:
A) Tyranitar
B) non-STAB rock attacks
C) stealth rock
Stealth Rock fills (one could argue, rather unfairly) a small void in the current OU metagame in the form of omnipresent "rock-type" damage. Not all types are great offensively, but Rock is. Rock, however, is a terrible defensive type, so not many rock types can overcome this to regularly compete in OU/BL. Even so, this is NOT perceived as a problem that needs to be "fixed."
Nor is it all that relevant... but I found it interesting.
And despit being [butthurt], the point I was trying to make was that I'm not even entirely sure what we're trying to see in testing Stealth Rock. And I'm asking for a noncondescending answer, which I assume other users could provide here. The best I have come up with is that the introduction of these SR weak pokes would somehow balance the meta into that perfect state that everyone seems to believe exists.
More or less, you've answered your own question. There is nothing universally agreed upon as "wrong" with today's OU, but there are some things that are a concern:
A) Garchomp taking 2 pokemon to "counter."
B) Deoxys-S
C) The perceived over centralization of Stealth Rock
Option "C" is unprecedented. People woke up one day and thought, "hey, you know what? why is it fair that certain pokemon types take 50% damage upon switching in? And this takes ONE TURN to set up? And there is no worthwhile method for eliminating it? Wat." I think it's a legitimate concern.
Game Freak hasn't exactly proven to us that they are architects of an overarching metagame -- the banning of certain nonsensical legendaries goes some way to prove this. Neither has Nintendo, which continues to have truly odd rules for any tournament they sponsor.
WE are the architects of a more perfect, more balanced metagame. We boast the largest variety in top-level competition. If we the people decide that Stealth Rock may or may not be fair and needs TESTING, then why argue? Smogon has never been a proponent of banning things without testing! Hell, there's even talk of reinstating OHKO moves or the evil of Double Team!
Anything goes until it's proven to suck.