The c-stick can make smash attacks safer, yes, but its main use is for aerials since you are able to move one direction in the air with the control stick while using the c-stick to attack in another direction. Though up-air and down-air are particularly aided since it's a lot easier to avoid jumping and fast-falling accidentally.

The big analogue triggers also play a big part since you are able to accurately choose between a hard and a light shield. Both of which have their uses in different situations.

And of course there is the fact that all buttons and sticks are very close to each other which allows for fast button and stick input combinations with little effort. It is true that the Wii U Pro controller is not far behind in this regard, but that little extra is required if you aim for first place.

i guess people stilled played with it on Wii and will want to continue to use it going forward

you just need to get used to the new controller (in this case Wiiu Gamepad), be competitive  has notihgn to do with the  input method, your skills are the way you are or not competitive.

Well, analog triggers, for one.

Sadly yeah, it what make the Wii U controller (both gamepad and pro controller) feel like a cheap toy then an actual controller.

Because playing Smash Bros with other controllers just doesn't feel that right! GAMECUBE CONTROLLER 4 LYFE!