Nah man its easier than that, goku couldn't make it through the vault of glass. He has no ghost, no respawns, no dragon balls or outside help. It's just him if atheon teleports him the fight is already over. He could instant transmission but atheon probably wouldn't be there since atheon teleports you to the past. Not to mention he doesn't know about the oracles or the relic. Gokus is toast. I'm a huge DB fan but I seriously can see him winning that one.