Ignoring the mostly (keyword here, there are definitely some convincing arguments here; they're just in the minority :/) terrible arguments in this thread I'll post my thoughts.
Ever since I first started hearing complaints about Greninja when ORAS came out, I still held the views that I did during late XY where I found Greninja to be extremely good, but not overpowered. As time went on, however, I started to see how Greninja had an unhealthy presence in the metagame. I found that many of my balance. Teams had to be reworked to not be 6-0ed by Greninja (and by 6-0ed I mean 6-0ed with minimal team support like VoltTurn and rox n shit), which was not fun as they were otherwise solid versus the rest of the metagame. Whenever I was making a balanced squad I always had to deviate from my original ideas simply because I found that many common cores I used were shat on by the frog. Even simple FWG cores like tran / bro / Celebi | ches, which handled a lot of the metagame, were falling to the standard Greninja set of Low Kick / Ice Beam / Dark Pulse / Gunk Shot.
And that's when my views on Greninja started to change. I found myself resorting to hyper offense more often than not, simply because the playstyle allowed me to dictate how matches would go from turn one. That might sound fine and dandy, but HO never was my favorite play style, and even ignoring that HO is really match up reliant. I used HO to improve my matchup against Greninja (ironically, the team I use doesn't even have Greninja, lol). I had to resort to a play style that I wasn't entirely comfortable with, simply because of one mon. Hell, for a time I was even using stall, simply because I hated seeing Greninja in the team preview and knowing that I'm in for a tough battle (btw I fucking hate stall, which goes to say something at the very least). However, this leads to my next point, which as a heads up, might seem a bit confusing at first.
Despite what I said above, I still do not hold the view that Greninja is overpowered. I say this because as I stated above, HO and stall both match up well against him, contrary to popular belief. HO May not have switch ins for him, but HO doesn't have switch ins for a lot of things. HO just has switch ins for mons that are very common and somewhat exploitable, such as Latios or Scarf Lando T. Hyper offense is an extremely high risk high reward play style that is hit or miss, and Greninja doesn't change that more than any other mon. I'd even argue that Mega Lopunny is worse for HO due to Fake Out, Scrappy, and an even higher speed tier. The other playstyle I mentioned was stall, which simply does not give a fuck about Greninja in the slightest. Chansey is a staple of stall and counters all non CB Low a Kick variants of Greninja (lol pls don't run that unless u like giving out free wins). No matter what anyone says, Greninja has no way of breaking 252 / 252+ Chansey that is played competently. Any competent player can beat a Greninja if all it can do is 3HKO the mon you send in. Despite her passiveness, she won't lose to Greninja. And even then, SpDef Mega Sableye is a thing (and trust me it's really good as it handles other things than ninja!!!), as well as Tentacruel, Alomomomomomomola, Mega Venusaur, and Suicune. All of these are common / relatively common stall mons that beat ninja and when paired up with other stall mons, fare well against the rest of the meta. Greninja can't break these mons and will kill itself through LO recoil before it can crit its way through according to the law of probability.
One last thing before I wrap this up: balance isn't helpless against Greninja. Despite what I said above about having to give up playing balance, I've still seen balance squads fare well against Greninja. Teams that feature mons like AV Conk, alomomomola, Bulky Mega Scizor, Ferrothorn, Tentacruel, and Chansey all have ways of beating the frog. It may be difficult, but the possibility is still there. It just takes creative teambuilding and the ability to make plays. I struggle with Greninja when playing Balance because I lack the creative teambuilding skills that other, better players possess. Regardless, Greninja is still a threat to balance and is definitely centralizing to the tier.
Now, that last sentence is important because that is where my stance on the issue is and where my vote will lie once I achieve reqs. As anti ban as this post may seem, I still hold the view that Greninja should be banned from the OU tier. I do not find him OP. I find him unhealthy. I find him unhealthy to the point where I feel pressured to play with teams I would otherwise use as little as possible. (Such as stall or some HO teams) just so I don't feel insanely pressured whenever I see Greninja in the team preview. Greninja limits teambuilding and limits it in ways where certain cores and mons simply do not work because he singlehandedly renders them obsolete, where they would otherwise fare well against the rest of the metagame. My experience on the suspect ladder confirms this, as from the games I have played so far I have enjoyed the tier a lot more with Greninja absent from it.
Greninja, your my second favorite mon, and it pains me to say this, but it's time for you to join your fellow starter (Blaziken) in the Ubers tier, as OU simply is not ready for you yet. I have to vote ban.
