Mill... heh. I haven't seen one of these in a while. I used to play a mean mill back when tsukuyomi was still legal. I miss that card... lol
Anyway, however much I like the card, I just can't see drastic drop off being that helpful here. You're already forcing them to draw with dark bribe, defender, card destruction, morphing jar, and hand destruction, and they still get their normal draw phase plus whatever draw cards they use. You aren't stopping that much from happening, really, especially considering they get to choose which card to toss when they draw more than one.
I also can't say I like offerings to the doomed much, as weakening your own draw power is never a good thing.
Then you've got gravekeeper's servant. If they're attacking... aren't you... dying? I can't see that card ever depriving your foe of too many cards in a duel, and by that time you would be dead, and that's assuming you get it out first turn. I understand that it punishes them for attacking your flip effect monsters, but it seems like you would just get swarmed if you're not actually stopping their attacks.
I was gonna say something about defender in here, but now I can actually see it working fairly well.
Nightmare's steel cage only stalls for so long. I'd much rather block with something that lasts, such as messenger of peace. Even though monsters with 1400 or less atk can still get through, there aren't too many of those out there nowadays, it seems, given the more aggro nature of the metagame, with a lower reliance on flip and field to graveyard effects.
Here's what I would probably do with that deck:
-2 Gravekeeper's Servant
-2 Offerings to the Doomed
-3 Nightmare's Steel Cage
-1 Stumbling
-2 Drastic Drop Off
+1 Night Assailant
+1 Sangan
+1 Des Lacooda
+2 My Body as a Shield
+2 Hammer Shot
+3 Messenger of Peace
Night Assailant should help you get back those flip effect monsters once they get sent to the graveyard, and sangan can fetch any monster in your deck. My Body as a Shield is great for stopping effects that would destroy your monsters before you can flip them, and one can even take down a dark armed dragon if it's stupid enough to go for your monsters first, and it should also help with zaborg, too, not to mention turning defender into a nearly untouchable fortress with one of the block attack cards down. Hammer shot should make up for the lost removal from offerings to the doomed. Des Lacooda should help with your draw power a bit, unfortunately it needs to be flip summoned, so no desert sunlight tricks. It's not a quickplay, but at least it's removal. I opted for a third messenger over a third stumbling, but there are probably a few other cards you could take out instead. I also would've liked to include a couple penguin soldiers for reusing already flipped monsters (although it's probably too slow in this format, anyway... not saying that this deck in general isn't slow >_>). I'm personally not a big fan of snipe hunter, but I understand why people like it, so I left it alone.
You're gonna need a bigger sidedeck than that, but I really suck at building sidedecks, so I'm not gonna even try to make suggestions.