Regarding your palm muting... if you notice, the original piece has palm muting that is more percussive...
Your muted chords overlap one another...and makes the piece less agressive... I think that might not be the desired effect...
I think that your palm mutes are either too near the bridge, so the strings vibrate a lot more than what is necessary... either that or your picking is not percussive and sharp enough...resulting in a kind of strumming effect...
My take would be that your muting should be closer to the neck, so the strings don't vibrate too much and your pick attack should be heavy.... then the rhythm will be tigher....
On the other hand, tone does play a part in making your muting sound more aggressive, so I could be wrong in my assumptions... heh...