It's tough to come in here and say Ganondorf is the worst character because you have to know that you're going to be bashed, attacked, and mostly liked be called a scrub. You'd be naive not to expect this.
However, I think I may have to agree with that statement. I don't suck with Ganon either: I know what moved are and aren't playable, and I rely on this strengths. However, his strengths don't even come close to outweighing his weaknesses. Let's examine his move set, and I'll break it down into usable and unusable:
Usable:
Neutral A
D Tilt
F Tilt
F Smash
D Smash
Nair
Bair
Dair
Uair
Side B
At this point you must be thinking, yeah, that’s a great selection of moves! Wrong!
Unusable:
U Tilt
U Smash
Down B
Neutral B
Fair
So, 33% of Ganon’s moves suck. When you’re opponents knows this, you have less variety at your disposal, thus making you 33% more predictable. Don’t think these moves suck? I’ll explain why they do.
U Tilt makes you painfully vulnerable, something Ganon is without even using the crap moves. U Smash has a relatively small hitbox, especially on either side of him, and since Dair’s usually have priority, it simply doesn’t help. Down B is slow, doesn’t do much damage, and even if you hit an enemy with it, they can still potentially his you afterwards because of the lag at the end (it also sends you upwards instead of to the left or right, so it rarely even kills!). Neutral B sucks for the same reason U Tilt does. And finally, Ganon’s great attack from Melee, the Fair, is now dreadful because of the almost unavoidable landing lag.
So know that we know which moves suck, one must also realize that Ganon gets camped on very, very easily. What can he do about it? Not much. Jump -> Air Dodge repeat works decently. However, due to his horrific speed, the camper can easily grab you, thus creating Hell.
I still play as Ganon, but you have to realize how disadvantaged you are if you choose to play Ganon.