I think Prime is a bit too quick to doom both races. In the first movie Prime wants to die with the cube in his chest. Okay that's fine but since Starscream took out the air cover who was going to stop Megatron from flying off to get repairs then coming back to pick off the remaining Autobots when he felt like it? By the second movie we wouldn't have a Prime to stop the Fallen so not only did Prime doom Cybertron in the first movie but his death would have doomed the humans as well in the second movie. It seems like Sam is the real hero is all of this since he stops Prime from his horrible plan in the first movie and he's willing to give up Bumblebee's protection to get to Prime in second movie so that Bumblebee can keep his parents safe. Plus Sam is one of the few characters who plan does not involve a lot of killing.