Thing is, stealing the Surfer's powers was a good plan, something that I'm pretty sure Doom did in the comics once. Problem is, that was his whole plan. He didn't seem to have thought about what would happen when Galactus actually did arrive to destroy the planet. Was he just going to fly off into space and let the earth be destroyed? Was he just gonna stay and get eaten? What if Galactus decided to make him his new herald? If there was more to the plan, like maybe following it up with stealing GALACTUS'S power as well (ala Secret Wars). Then the FF could foil THAT plan, thus saving Galactus from destruction, and in return Galactus would spare earth.
Watching this and SM3, I wondered if the writers were on their way to making good scripts, until the deadlines were moved up and the studio was just like "Okay, wrap it up. We'll shoot whatever you've got so far."