1. His teleports are at given intervals. He has a few seconds to blow him away. He wouldn't need to charge an outrageous attack to kill Atheon. 2. He could just nuke the Vault from the outside. While we, the Guardians, have to go inside to kill Atheon; what's stopping a superior force from just destroying it from the outside? According to lore, Atheon, the Gorgons and the Templar are useless without the Vault. 3. I don't think teleporting someone to the future and then summoning oracles in the past would do anything. They need to 'see' you to erase you. 4. He could just skip all this and destroy Venus outright.