Calamity ganon was just ganondorf's puppet. The hand holding him down was a Sage's hand that literally locked him in place. Likely one of Zelda's ancestors.
It will be Ganondorf, after failing to reincarnate via his puppet to escape the prison he's in deep under hyrule, uses the strength he gained from Calamity ganon to break free and revive himself from a half-death. He will be far more powerful than Calamity ever was.
Just remember: this is the same guy who has outright destroyed the world before, and has literally altered reality. Calamity ganon was weak compared to his past forms.
His strongest form was A link to the past. he actually got his hands on the triforce, could possess people, altered an entire reality (dark world was the realm the triforce actually existed in, and wasnt always the dark world)
In twilight princess he took over the twilight realm.
Calamity ganon just sperged about and wrecked shit.
Ganondorf coming back means very bad things. It also might be why calamity ganon was such a chump boss fight.
My only gripe is this is shaping up to be $70 DLC if it uses the same map from BOTW.
If ganondorf comes back and does his ALTTP or twilight princess treatment to reality, we may get a game that is fundamentally different.