Optimus Primevil wrote:maybe the allspark fragment acts as a downgrade for megatron?
Prime was likely holding back in the first movie due to all humans around and buildings to wreck. He didn't seem to really want to kill Megatron, as he offered have the Allspark merged with him rather than Sam's idea(Sam said he was never giving him the all spark...so much for that theory heh.), and really seemed saddened by Megatron's death.
Not to say Megatron was rebuilt from the best parts as his other hand was rather gimpy compared to his original one. Doctor might have done a bit of a rush job in ROTF. Megatron was still incredibly durable for first two films, as he withstood. The 3rd film he'd been pushed to the brink, from all onslaught he'd received.He took a volley of attacks from the air force, army and Optimus (and some minor damage from the other Autobots.) prior to the Allspark being shoved down his chest.
In Rotf, Megatron probably takes a worse beating overall, and keeps going like a champ. He smashes thru a submarine like it was nothing. Withstands all abuse from Optimus, and kills him in the factory/Forest battle.(with help, but in the end Megatron kept his eyes on the prize while Prime got sloppy.)In the Desert battle Megatron gets blasted something fierce by the armed forces. He takes a massive volley of shells and a bomb that trashes every one caught in the blast but him. (Ironhide was the only other Transformer who survived the blast and he was seriously damaged by it.) After killing Sam he still manages fly away after all that. Then takes on a powered up Jet-Optimus, and overall fairs better than the Fallen did. For a moment I thought Prime killed Megatron again...till he yelled for Starscream of all people.
All in all Megatron was a beast for first two movies in terms of what he could take. It made sense for him be off his A game and rather weak based on his condition in Dotm. While people might have wanted a final throw down for him and Prime that lasted longer, neither was remotely close to full power by time they tangled. Basically whoever hit the other first was going win, and Prime took the first strike. I think if Megatron had blasted Prime then he'd easily won. Given how much his blaster took the wind of Sentinel's sails , I'm sure Prime would have been in trouble.
"The question that once haunted my being has been answered. The future is not fixed, and my choices are my own. And yet, how ironic...for I now find that I have no choice at all! I am a warrior...let the battle be joined." —Dinobot