Do you think that there should a a pokemon game like super smash bros?

Pokken Pokémon choices are based on popularity and what they want to promote in the main games as much as fighting viability or potential for interesting gameplay.

Kind of like Smash, really.

I think a Pokémon exclusive Smash would be very popular. And because it's a Nintendo property, we would presumably avoid most of the Smash-clone dialogue.

But I also think Nintendo would rather not compete with themselves. They would prefer that Pokémon fans buy Smash and use Pokémon characters, rather than dividing the playerbase.

Furthermore, who would make this game? Would it be Sora?

It's kind of similar, except you can level up characters after using them enough, then you choose where the stat point you got from levelling up goes.

Also, the arena switches between being 3D and 2D sometimes while fighting (can't remember if there was an option to set it to be only one of them for the entire fight), unlike SSB where it's always 2D.

Also, there was a story mode where you fight NPCs and their Pokémon to get into better leagues (D rank, C rank, etc.) and encounter a mysterious dark Mewtwo every time you rank up (which later on becomes the center of the story).