I never considered novelizations canon, personally.
My alternate explanation (read: better

) states that Megatron is a Prime decedent just like Optimus (they are brothers). So Megatron is perfectly capable of taking out Optimus (as per the Primes kill Primes concept). Also, consider that the Primes are the first, and most powerful, of the Transformer race. It would seem that older Transformers had more power in general (Fallen and Jetfire, TFs from the past, can
teleport). So I'd say the only person closet to beating Fallen would be Optimus by default - a naturally stronger TF due to his Prime lineage. And, just being abstract here, Megatron as well (I wouldn't put the action past him either).