^This guy said it.
If you don't have a projectile or a good disjointed attack that hits downwards, then oh well. Let's look at the top tier:
MK: LOL i'd love to see someone plank MK
Snake: Nades, C4, even Nikita timed properly
Diddy: Nana z-drop
Falco: Pretty sure his Fsmash is disjointed enough, not sure about Ftilt and Dtilt
Ice Climbers: well timed ice blocks (though fighting plankers isn't their strong suit)
Marth: If they plank long enough, that huge disjointed sword will make them regret it
Wario: Not sure what he does about plankers actually
DDD: He's got mid-air jumps - he'd prob go for a stage spike, Ftilt if they're not being careful about how high they rise
Pikachu: PikaCHU, PikaCHU, PIKA! (Jolt and Thunder)
Olimar: I can grab people from below the ledge ![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
So those are the top ten, and most of them have ways to deal with plankers. If people are covering the ledge so it can't be hogged, they're in range. If they're dropping down, they can get ledge-hogged (not to mention several of these characters can still hit them down there).
And I didn't mean that the ledge was always a bad place to be in. I meant it's a bad spot to stay in indefinitely, because if you give them long enough good characters will punish you for it. Pit and G&W don't have moves that are short enough to allow them to regrab the ledge before their invincibility runs out and cover the area at the same time. That's why MK is the best planker - you can stop the other two. Sure, some characters have problems with it, but people also have problems with Nado, lasers, pivot grabs, chain grabs, air camping, etc.
None of the options you mentioned above actually do anything to stop ledge grabbing as most of the options you mentioned above give the ledge grabber enough time to get back up on the stage and punish the other player for doing some dumb laggy attack on stage.
MK: this is the only one I kind of agree with but I still think that It might be somewhat risky.
Snake: suggesting the Nikita missile made me laugh. all the opponent has to do once you use the missile is air dodge it and punish you for going for such a stupid option . If this truly worked, we would see Ally or Razor use this move to hit all the people grabbing the ledge. C4 gives the opponent more than enough time to get off the ledge before it detonates and puts snake in a bad position(above his opponent). Grenades won't work since all you have to do when your opponent pulls one out is jump back on stage. Holding a grenade limits snake to only his B attacks.
Diddy: nana Z drop gets caught and thrown away faster than didy kong can pick up a banana to punish his opponents actions. Its a bad Idea.
Falco: His F-smash will not be able to hit an opponent that knows how to edge grab and make it so that they snap the ledge. Neither will any attack that falco does on-stage.
Ice climbers: their projectile is probably the only projectile that can successfully stop characters that know how to ledge grab because they throw two projectiles instead of one. They are however skrewed against characters with multiple jumps that play on the ledge.
Marth: has the same problem as Falco.
Wario: has the same problem as Diddy kong except his tires suck way more as they are harder to take out.
Pikachu: his projectile is good but, vary slow. by the time the second jolt comes, the opponent will be on stage and ready to punish you
Olimar: his grab has the same problems as Falco's and marth's F-smash.
These options you gave are really bad(even though some of these are the only options that these characters have other than jumping off the stage) and do not work when done on a player that knows what he is doing.