"short time the developers were given"
Considering they've stated that they started "working" directly after Brawl was released, I doubt it. 7 years is a good amount of time to develop a fighting game.
"bowser Junior’s code was finished three days before the game released"
That's bullshit.
By that time, the game has gone golden and is waiting to be released.

Actually, smash four was always intended to have DLC, as, because of the short time the developers were given, they barely got the content included done (bowser Junior's code was finished three days before the game released)