We killed Crota in his realm, were he is vulnerable. He is immortal outside of his realm. The fight couldn't take place in Crotas realm as it would have to take place in the vault of glass as atheon, the Templar, the oracles and the gorgons cannot exist outside of the vault. So that means atheon could easily win the fight by himself by willing the entire dragon ball z universe out of existance.

Are you daft Atheon can't just warp it out of existence. Templar, Gorgons and other vault Entities can exist outside of the vault you dumbass