The metagame revolves around the changing use of particular options. By analyzing this through actual gameplay or by watching videos, one can break down the possible options the opponent has at his disposal. Nothing(very little) should be new when you fight a person. If you consider yourself a good player, you should have a good understanding and knowledge of what the person is going to do and how they will counter you based on your options and their knowledge that you also know what options they have.
Of course, at any time a person can have a novel idea and create new options, but this is typically rare and often these ideas start with much higher level players that then get passed on to the scrubs.
Competitive fighters are just matches of the mind between the two players.
Brawl is alot about safely restricting options because fewer options for my opponent makes it easier to predict what they will do.
I know he can pick 1-4, and I can predict which one he can do; or I know he can pick 1-2, and I can more easily predict what he can do. Planking abuses the limiting of options in a way that no one option can. By going into a match I know what my planking options are and his options to remove me from the ledge based on experience and knowledge of the current metagame.
I would say the planker has more options (by this I mean more SAFE options). Still, even the planker limits himself through planking.
It just so happens that in limiting both himself and the opponent into having fewer options, and doing so while on the ledge, puts him in a much favorable position.
While you might have near the same ammount of options, a single move option from the planker can typically cover a wide array of the other characters options. (one argument used in order to have MK banned since his options cover everything) It's rock paper scissors where I pick rock and rock beats both paper and scissors. When competitive fighters are supposed to be a game of the mind, planking essentially turns the game into the above mentioned rock paper scissors. Hope you play a character that can get someone off the ledge. Hell even Metaknight could not remove another Metaknight from the ledge.
Planking essentially removes and limits most of the thinking person has to do in order to win.