TFA Megatron never got emotional. He never made rash decisions or failed to think something through. TFP Megs was too hasty, and often made very poor decisions based on in-the-moment emotions or short-term gain. Killing Dreadwing was hasty and foolish, and he would've been better off letting Starscream die as the Decepticons didn't suffer at all from his absence, nor did they prosper from his being present from that point on. He killed the Predacons because he was afraid they'd turn on him, which only served to cause Predaking to turn on him. TFA Megatron was very opportunistic and thought things through. He only disposed of assets if they'd completely exhausted their use, and actually tried to win over more potential allies than he did remove potential threats. Had he not thought so lowly of the Autobots (which is understandable, they're basically power line technicians and he's the supreme leader of the most powerful army) I could even see him trying to coax them into aiding him. Not that Optimus would ever believe him, but the thing is that's TFA Megatron's MO. He thinks, he explores avenues other, lesser leaders like TFP Megs would foolishly overlook. Combine his proactive attitude, his patience, and his intelligence, TFA Megatron is a far sharper sword than TFP Megs. And that's on top of him being physically superior, just based on their observed feats of strength, speed, and endurance.