I don't know if you are being dumb, sarcastic, or just trolling... I'm pretty sure the last one because no one can be that dumb.
Anyways
1, 2, 3, 4: I already explained this like 3 times and you are saying the same stuff al over again... so im not eve bothering
8,4/10 Is above average, and I said that with THAT team I have that win rate.
I ussualy win about 9,2/10 in Singles and about 7,9/10 in VGC (Im still learning the doubles format
)
And about you Greninja question. You can't decide who is good or who is bad with a single question that even someone that doesn't play Pokemon can know by just looking on Google... and probably the "correct" answer is going to be conpletely based in your opinon, making the question even more usseless... anyways:
First you didn't said what format was (Singles, Doubles, etc) or the moves it has, or even the nature and Ev Spread, second, the ideal Item depends on what your team needs...
Good items for greninja could be
Life Orb with Naive, max Speed, 44 Atk and the rest in SpA, so it can OHKO Azumarril with Gunk Shot, or
2HKO Chansey with Low Kick
Focus Sash with max Speed and Max SpA for a Offensive Lead
Even Expert Belt or Choice Scarf (to outspeed 145-150 Spe Mons) could be a good idea (If you don't like Life Orb, since is such a baaaad Item, isn't it?)
Anyways, I'm not going to take seriously what you are about to say about me, because I'm pretty sure you are a troll or the worst Pokemon player in this side of the Mississippi, and is going to be based in your "completely accurate knowledge" about the metagame
Goodbye