My argument for my grenninja should stay in the tiers is simple. Yes it can ko many things in the tier yes it is unpredictable but so are most sets.Ape for example is a very good mixed a tacked thus making it unpredictable does that mean it should be banned.
The current meta is sandrush the speed of grenninja let's dark deal with it much better. And from personal experience water is less able to hit it hard. Greninja had coverage for things that water has had issues with such as mega venasure ferrothorne and if it stays mega metagross. It is one of the few checks or counters for these in the tier. It does not take any hits and has zero form of recover and relies on constant switches in order to get a decent match up.
As for mega metagross the ban makes no sense with the current meta of ground and flying. It hits hard and has some good defense but where it falls is it cannot take any special hits and zero recovery.
Sorry about the spelling I am using my phone
I'm sorry, but some of your arguments are simply untrue. First of all, most of the mons used in the current meta have a very predictable moveset, i'd say a fifth or so have unpredictable sets.
Second, you say that the current meta is sandrush, so i'm assuming you mean that greninja is needed to deal with ground, and more specifically, excadrill. However, dark (and water for that matter) have access to a certain, often overlooked pokemon called crawdaunt.
252+ Atk Life Orb Adaptability Crawdaunt Aqua Jet vs. 4 HP / 0 Def Excadrill: 359-426 (99.1 - 117.6%) -- 93.8% chance to OHKO
There is no way in hell that an excadrill would stay in on a crawdaunt. Greninja is actually only able to beat sandrush exca when scarfed, which means you have to guess regardless (whether the ground player switches to gastro or not). I will agree with you that water has a hard time with dealing with mega venusaur (bounce gyara is the only thing that comes to mind
252+ Atk Life Orb Adaptability Crawdaunt Knock Off vs. 0 HP / 0 Def Mega Metagross: 270-322 (89.7 - 106.9%) -- 43.8% chance to OHKO
252+ Atk Life Orb Adaptability Crawdaunt Crunch vs. 0 HP / 0 Def Mega Metagross: 333-395 (110.6 - 131.2%) -- guaranteed OHKO
0 SpA Tough Claws Mega Metagross Grass Knot (60 BP) vs. 4 HP / 0 SpD Crawdaunt: 194-230 (72.3 - 85.8%) -- guaranteed 2HKO
You will forgive me however, if I do not sympathise with water's inability to have an incredibly convenient answer to a threat from one of the weakest monotypes in the metagame, that also happens to be one of water's 2 weaknesses. If you look at other types, you might notice that actually most of them have a similar threat that needs to be dealt with, usually using multiple pokemon. In bug's case for example, Charizard-x is incredibly hard to deal with, as it is practically guaranteed a sweep if it gets a safe switch in to any pokemon that does not immediately deal with it in some form or other. Bug however, does not have some be-all end-all check to it, as unlike venusaur, Charizard has the potential to become both strong enough to OHKO every bug and faster than any check with a single move. Bug teams basically have to play carefully around this huge threat, but that doesn't make it impossible to beat. I believe a type as well balanced as water has a much easier time to do something similar with mega venusaur, without needing something that can always be used to just kill it off if it takes a little bit of damage, with very high consistency.
As far as banning mega metagross goes, I hope your opinion isn't too biased because you believe that greninja's availability in monotype might be affected by whether megameta is banned or not. Mega meta is actually pretty good against flying and ground, as far as megas go for steel, and on psychic it's about average. I'm not saying that this means that mega metagross deserves a ban or definitely needs to stay, but it definitely has one of the strongest influences in the meta, as it practically destroys types weak to steel. Granted, this is practically unavoidable when facing steel regardless, as the most common alternative (mega scizor) does essentially the same. I believe it at least deserves a suspect test at some point in the future.