Well, I went into some detail earlier, although I don't know if you caught that post. I'll be happy to go into some of his safe options, but first let me reiterate some of the points I made earlier.
1) He has an unusually easy time planking, while still avoiding breaking any edge grab limits. He is also at an advantage on the ledge whereas most characters are at a disadvantage.
Planking is banned at most tournaments (all AL tournaments I've been to). Besides, he's not the only character who can plank well. Marth, Jiggs, even Falcon can plank pretty well.
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2) He breaks edgehogging on stages where he can glide under the bottom and grab the other edge if he misses.
Addressed already, that doesn't "break" edgeguarding because he's not the only character who can do that. In fact there are quite a few characters that can go under the stage if they're having troubles getting edgeguarded.
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3) His recovery is phenomenal. He has five midair jumps, 2 glides, and all 4 special moves that have excellent recovery potential.
This has no bearing on whether or not he's a "broken" or bannable character. It just means that MK will not likely be gimped and that he'll probably be getting back on stage any time he's off. He's still limited in his recovery, just not as much as say Ganon. Anyone who has ever played a good Samus, Peach, or Jiggs knows that this isn't really a novel concept to smash bros.
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4) He has no bad matchups and no bad stages. Counterpicking is part of brawl whether you'll admit it or not. It's there to balance the set in case one person feels they could do better with a different matchup if they lost the first round. Counterpicking has been part of smash tournaments since the first game. Although precedent in other games may be different than this, we should rely on precedent from our own series first. When a MK goes into a set, that player has a guarantee that they will have at worst an even matchup and will not play on any unfavorable stages. No other character in the game has that luxury.
This is the only legitimate point you've brought up so far. In smash bros history it's not like this is a first. Melee Sheik was close to MK in this regard, but 64 Pikachu surpasses MK completely. You want smash bros. precedent, you got it.
Besides, you're putting way too much weight into character matchups than you should. At the level of competition we're talking about character matchups kind of melt away in the face of player matchups.
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Now then, the reason I say Metaknight has lots of safe options is because he has tons of virtually lagless high priority moves. He can cancel the lag from his shuttle loop, tornado, and drill rush, which all have lots of priority and lots of knockback where shuttle loop is concerned. He has a super fast and long range down smash. 4 of his aerials are lagless and high priority, where nair has some lag. His down and forward tilt are fast with priority and range for the ftilt. He has glide attacks from the glide and shuttle loop that will knock you back too far to shield grab AND can be comboed into down smash. My point is that MK has an abnormal amount of safe moves that aren't punishable except when the player screws up.
"Cancelling" lag on side b is extremely situational and also too risky for any MK to ever use it. Not to mention in order to cancel the lag you have to be in a very specific location. Even if it's "virtually lagless" if you know where they're going to be at the end of it you can punish them very easily, which completely defeats the purpose.
And mach tornado you can reduce lag on, but it still has lag.
Actually the only move that is practical to reduce lag of his specials is the shuttle loop.
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The question isn't whether Metaknight is beatable. Metaknight is obviously beatable as displayed by great players like Ally. The question is whether MK ruins certain aspects of the game enough to ban him. Think about everything in the game that we ban. We ban items. We don't ban items because you can't win with items turned on. We ban items because they detract from what the majority of players believe should be the focus of the game. We ban stages. Just like items, stages can take away from what we believe to be important in the game. We ban stalling. We ban stalling because it takes away from the fighting, which is what we perceive to be the most important aspect of brawl. It takes skill to use items effectively, do well on banned stages, and it even takes skill to stall. It takes skill to use Metaknight at mid and high level of play, but he decreases the quality of the game because he detracts from other aspects we deem important: mindgames, spacing, tech skill, etc. He decreases the importance of these aspects just as items or a funky stage would.
You might honestly believe that, but it only serves to make you look inexperienced in high level play.
All that other stuff about banning items and stages to make the game playable doesn't apply to Metaknight.
At all. The difference between banning hammers and banning metaknight should be painfully obvious to anyone who plays smash at a competitive level. Trying to make that argument comparing the two basically subverts the quality of every other thing you said on the subject because of how obviously wrong that comparison is.
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I just dismantled the entire pro-ban MK argument in 20 minutes.
Congratulations.