You stated that a 64MB block would give control of the blockchain to the bad actor. This is wrong because as soon as the bad actor broadcasts the header every other miner is on an even footing.
You are forgetting that it takes time to broadcast 64MB (so they could have already mined the next block in advance) and if others are not going to bother validating (which as stated would likely take them more than 10 minutes) then they could easily be tricked into mining on a fork.
It should be noted that the larger that you make the block size the easier such an attack becomes.