Inconsistency of the ROTF Movie with the Prequels

In the comic prequels we see that the fallen is sealed away by his brothers in another dimension and is communicating with megatron through his sacrophagus, how come he broke free in the movie (no explanation given)? Also , in the prequel nothing is shown that the decepticons know of the existence of the fallen yet in the movie it seems he is already leading the decepticons. THe movie have therefore so many unexplained parts that don't tie well with the comic prequels. Hope someone could explain this to me. It is also strange to me how come so many primes cannot defeat the fallen, while just one prime eliminated himin a matter of minutes.