Let's just take a look at MetaKnight for a second, and his Qualities. Starting with his Pros
- Best Recovery in the game
- Best Edgeguarding in the game
- Best Attack Speed in the game
- Best OoS Options in the game
- One of the best Combo Potentials in the game
- Excellent Damage Collecting Game
- High Priority on all attacks
- Great Range
- Tornado is one of the best moves in the game, with very few practical counters
- One of the fastest ground movement speeds
- Great KO Options
--- Doesn't help the fact that all of his killers (Except Fsmash) is practically lagless, and very hard to defend against
- Good Air Resistance
- Is pretty small
- Looks Awesome!
And his cons....
- One of the Lighter Characters
- One of the Slowest Airspeeds in the game
- His Air Break from a Grab can be Exploited from a few characters *CoughYoshiCough*
You can't deny that he's overpowered by a considerable amount. It also doesn't help that against most characters, he has absolutely no weaknesses that can be exploited against him. Nobody in the history of Smash had this many strengths without a considerable amount of Weaknesses to balance the scales.
Comparing to the next characters to come in Line (Snake, Dedede, G&W), they all have considerable amount of weaknesses to counterbalance their strengths. MetaKnight has nothing! Even Melee Fox had Weaknesses anyone can exploit!
Granted he might not be as broken as Akuma, but he's still overpowered, especially compared to the rest of the cast. Hell, compared to the other games, he's even doing better dominating their game better than Yun or Melee Fox! I don't think there's a current Fighting game where a Top Tier Character is dominating on the same scale as him.
He's just Broken, it's as simple as that!
Done writing, Tired, Sleep now