I wouldn't change your army too much if it's working. If you'd like to get the duke in your list, which I think might be a worthy endeavor, you could do so just by swapping out the haemonculus and 1 unit of wracks(perfect point swap).
That would give your wyches upgraded combat drugs, and give your army the ability to deep strike should you choose to do so.
Now, obviously, you'd need to swap out the other 2 wrack units for kabalites, which you could easily do.
2x 3 wracks in a dual cannon venom = 190
2x 5 warriors in a raider = 210
So you'd just need to free up 20 points. I might consider dropping the reaver jetbikes for it. This would allow you to get 1 of the warrior squads up to 9 guys(duke goes here), with splinter racks in their raider, and either flickerfields or night shields on both the raiders.