Only in TF1 did we get a real main decepticon threat when megatron was at his best

in ROTF megatron was handicapped from old decepticon parts making him slower, the fallen seemed like an ageing prime that did nothing for decades

while DOTM megatron was a shadow of his former self who became more of a plotter than someone who would go into battle, shockwave seemed to clumsy, soundwave and lazerbeak were fantastic.

So we got 2 sides of the scale in TF1 and DOTM

 

The highlighted portion of your comment made me lol. I really don't see how the Fallen was so easily defeated. He's got telekinesis and the power to travel through space bridges at will.

 

Time limits. The writers said that even they were disappointed with the end battle.

 

Look at TF1 megatron, and DOTM sentinel, they were very difficult to be damaged when ever optimus tried to use all sorts of combat moves, from weapons to fists etc he was struggling against these 2. While the fallen did look like he was falling apart at times, before optimus became jetfire he seemed fearful of challenging optimus, that he needed a weakened megatron rebuilt from weakened decepticon parts to do his dirty work