Yes, the blockchain work has nothing to do with time. I still don't think this is an exploit and it's annoying because many exchanges have bought into it and are asking everyone to upgrade needlessly.
If you can drive the difficulty down you can generate a longer chain regardless of the power of the rest of the network. You could do this in isolation and then rejoin the main network and force a reorg. The exploit is very serious and if you pull it off, you can wreak havoc. Checkpoints wont help since you can rinse and repeat over and over and that much disruption to the network is simply a game over for the coin.